1) 本邦産シロレイダマシ属2種(シロレイシダマシ及びヒメシロレイシダマシ)の歯舌を記載し, 有舌腹足類の歯舌には, 顕著な雌雄差の存在する種類があるこを初めて明らかにした.2) シロレイシダマシ属の歯舌は, 他のアクキガイ科の諸種のものとは非常に異った形を示し, 又中歯の形, 歯列比, 中歯の巾と側歯の長さとの比, 歯舌の色等に著しい雌雄差がある.3) 従来, イガレイシ属の下におかれていたヒメシロレイシダマシの歯舌は, シロレイシダマシ属のものに一致するので, 転籍した.これで邦産のシロレイシダマシ属はシロレイシダマシ, ヒメシロレイシダマシ及びsiderea (Reeve)の3種が含まれることになった.4) シロレイシダマシ及びヒメシロレイシダマシ2種の歯舌の特徴を簡単に比較して表に示した.

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Larval shell equivalve, nearly oval in shape, slightly contracted anteriorly ; umbo projecting prominently, with 13-15 well marked concentric growth lines on the surface of shell ; ligament slender, situating internally at the central part of provinculum, which is small, reduced anteriorly with 4 teeth of rectangular shape, shallowly divided each into 2 parts at their tips, excepting a posterior tooth in each valve ; lateral hinge system reduced to a small flange on the left valve without any lateral teeth ; larva having a pair of eye-spots, dark in color without apical flagellum on the velum. Length of valve 245μ on an average of 15 specimens ; prodissoconch 253±16μ on an average of 100 individuals.

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1) 生殖期にヒメエゾボラを水槽で飼育観察した.その結果相当の頻度で雄同志の間に仮性交尾が見られた.2) 交尾のとき雌雄が接近するのは偶然であって, 雌雄の間に互いに他を誘導する感覚はないと考えられる.

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In 1956, the writer observed the breeding of Littorivaga brevicula (Philippi) at Asamushi, Aomori Prefecture, and Littorivaga atkana (Dall), in 1957, at Hakodate, Hokkaido, Japan. 1. Littorivaga brevicula (Philippi) liberated planktonic eggs with a transparent, colourless and helmet-shaped capsule. The capsule measures about 350μ in diameter, about 170μ in height, and the egg about 84μ in diameter. The larva hatches about eight days after the spawning at 10℃ through the concave spot at the center of the bottom of the capsule. The breeding continued from February to April while the snails were still living in the area from high to low tide. Nearly matured eggs and spermatozoa were found in the gonads of the snails exceeding 6.5mm in shell height. 2. Littorivaga atkana (Dall) liberated and deposited eggs in an ootheca under or at sides of stones near mean tide. The egg was contained in a transparent, colourless and egg-shaped capsule, in which it was covered by a semi-transparent substance. The capsule measures about 550μ in diameter, about 400μ in height, and the egg about 200μ in diameter. An ootheca includes about 120 egg-capsules, and several oothecas gather to form large masses. The breeding continued from January to February on the rocky coast of Hakodate.

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アラレタマキビNodilittorina granularis (Gray)は, 青森県浅虫においては8月下旬浮游性の卵を産むことを観察した.アラレタマキビは冬季は高潮線附近を離れて上部に集合する傾向が見られるが, 夏季は高潮線附近まで分布が拡大し個体数も増大する傾向が見られた.夏季の分布の拡大は繁殖に関係があるものと思われる.本研究に際しては, 東北大学臨海実験所長平井越郎博士の終始御懇篤なる御指導を賜り, また東北大学教授元村勲博士には貴重なる御助言を賜ったので, ここに深く感謝の意を表する.

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