The shell of Parafossarulus manchouricus scarcely shows sexual dimorphism, but the male shells appear to be somewhat more slender than those of the female. A transverse row of the radular tooth consists of 1 central, 2 lateral, 2 inner and 2 outer marginal teeth, and the cusps of these teeth show numerical variation in different individuals. The stomach is composed of two parts ; the anterior part is broader and provided with the gastric shield near the center, while the posterior part contains the crystalline style and its sac. The penis has a characteristic flagellum at the anterior third on the left side, but its function is obscure. A convoluted tube containing a mucous fluid is situated at the base of the penis and its opened end is at the tip of the flagellum. The vaginal opening is located at a fairly long distance from that of the oviduct ; the former is near the spermatheca at the apical-most part of the mantle cavity and the latter slightly posterior to the anus. The central nervous system is composed of 9 ganglia and the pedal system 2 ganglia. The vessels are feebly developed, while the haemocoele is well differentiated. The renal aperture opens directly into the mantle cavity at the apical part and no renal duct is recognized.

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Post-mortem drift of the Recent Nautilus shells by oceanic currents is exemplified by the materials collected from the west coast of the Malayan Peninsula and the Japanese Island arcs. Characteristics of habitat (H) and realm of post-mortem transport (T) in general fossil assemblages were schematically explained. T is composed of H, To and Tt, where To is the realm of postmortem transportation outer than H in usual condition, and Tt is the extended portion of To especially caused by an oriented agency of transportation such as turbidity current or strong oceanic current for instance. Thanathocoenose in H is tentatively called as quasiautochthonous assemblage being separated from the true autochthonous, i.e. orthoautochthonous one. Thus, allochthonous assemblage is defined as the dead assemblage out of H or the inner realm of post-mortem transportation. In short, there is an almost fixed relationship between H and T insofar as the areal distribution, and an inequality T>>H, where T=H+To+Tt, is given. The distributional pattern of T inclusive of To and Tt is also diagrammatically presented. Its general figure shows an asymmetry to the center of H. State of preservation, density of distribution and other g neral characteristics of a thanathocoenose should have a tendency to decrease as the realm becomes wider and wider. This tendency is named H→Tt declination.

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1. The criteria used by Zhadin (1938) as specific characters in Margaritifera (Unionacea ; Margaritiferidae) are valid. 2. All Japanese Margaritifera belong to M. laevis (Haas, 1910), known only in Sakhalin, Kuril Islands, Hokkaido and Honshu. 3. All Margaritifera in western North America belong to M. falcata (Gould, 1855), and are more closely related to M. laevis than to the species in eastern North America. 4. The salmonid fishes that act as larval hosts of these two species of Margaritifera are close relatives phyletically even though they are classified in different genera, Oncorhynchus and Salmo. 5. At some time in Tertiary a Salmo-like fish, acting as larval host, and a species of Margaritifera were found on both sides of the North Pacific, on island arc of north eastern Asia and on the mainland of northwestern America. After a separation of this range into two parts, the biological system fish-and-mussel changed at different rates so that the fishes are classified in separate genera, the mussels in separate species. 6. Host-specificity of the larval glochidium stage of Margaritifera to a young Salmo-like fish has been more persistent than the morphological attributes of the adult fishes. This is in correlation with the morphological similarity of young Oncorhynchus to young Salmo, and supports the belief that host-parasite relationships may aid in tracing phylogeny.

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Molluscs and shell-remains, 53 species in total, were obtained at 16 sampling stations of 25 to 500 m deep along the coast of Tagonoura, an area of the head of Suruga Bay. Bottom facies generally consists of mud except gravelly one of littoral zone, and locally has been strongly contaminated by residue of wood pulp, where molluscs are scarcely found. The species assemblage can be divided into 3 groups from their vertical distribution, i.e., those of shallower zone than 50 meters, of 120 to 160 meters deep and of deeper zone than 250 meters. Obtained species are composed mostly of mud dwellers of open coast, and no typical element of inner-bay was found.

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Seedlings of Haliotis discus hannai Ino were transplanted from the northern seas to southern areas and the effect on growth was examined. 1. Age estimation of the specimens of these abalones was performed by a newly devised method with much satisfactory result besides the usual one : namely, the surface of the shell is cleaned and the annual rings formed on the shell can be fairly easily looked through by approaching the shell above a red electric lamp used in the dark room. 2. Growth rate of the abalone has been compared among shells from the three localities, (1) Okujiri Island, Hokkaido, (2) Onagawa, Miyagi Prefecture and (3) Ibaraki Prefecture. It has become evident that those from locality (3) have a better rate than the other two. 3. Abalones (H. discus hannai Ino) show a tendency to turn to a typical form (H. discus discus) with a better growth rate by transplanting in the littoral of Ibaraki Prefecture. 4. Augmentation of average shell-length by transplantation is seen as follows : in the range of 1.7∿3.0cm in 1 1/2 years, 2.7∿5.0cm in 2 1/2 years and 5.3∿6.6cm in 3 1/2 years. 5, Similarly augmentation of body-weight by transplantation is seen as follows : 2.5 times in 1 1/2 years, 4.0∿6.8 times in 2 1/2 years and 4.6∿14.8 times in 3 1/2 years. 6. After transplantation, the abalones show as much growth rate as the native ones in 2∿3 years, and become a fishing object by attaining a capture-limit size (shell-length 11cm). 7. By estimating the total amount of augmentation based on the growth rate of the transplanted abalones, it is presumed that augmentation of about 6 times in body-weight can be obtained in 3 years.

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