53 



think it best to se[)irate them provisorily. At Suvugachii mostly t'rai^mLMits are 

 found, some of them with nice pearly lustre aii'l with traces of colonr-marlcings 

 on some parts of the shell. 



C'ytkerea meretviv Linne. 



(Syst. nat. ed. 12, p. 1132. — Schrenck, noviljapan. IMoll. p. 54.") to 550.— 

 Lischke, jap. Meeres-Coneh. v. 1, p. 122. and v. 2, p. 108.). 



Omitting the disciission ahout the liniits of this species, most unhappily 

 divided into a great many so-called species and varieties, and referring, like 

 Lischke, to Schrenck's statements on this matter, I classify the Cythereas of the 

 tertiary beds of the environs of Tokio according to these authors. I add, how- 

 ever, that according to other authors the name of tlie frequent Japanese Cythe- 

 renj, which are identical with the fossil ones, would be C. lusoria Chemnitz (Con- 

 chyl. — Cabinet v. 9, p. 337; Lauiarck, hist. nat. 2d. ed. v. Ti, p. 297: Uoemer, 

 Monographie d. Mollusken-Gattung Venus p. 30, pi. 12, f. 1), of which also 

 'sub-varieties' have been largely established. The triangular, posteriorly elonga- 

 ted form, the smoothness, the typical hinge and not very thick shell, in some 

 in.stances also slight colour-marks, are common to all the fossil shells. A few of 

 them, though very small or broken, were found at Surugadai. 



Cyclina sinensis (Linne) Gmelin. PI. VI. fig. 23. 



(Sj-st. nat. Linn. ed. 13, p. 32S5. — The name was altered into chinensis 

 by Lamarck, hist. nat. 2d. ed. vol. G, p. 291, Reeve, Conch. Icon. Artemis, 

 pi. 1, f. C, Sowerby, Thes. Conch, v. 2, p. GGl, Lischke, japan. Meeres- 

 Conch. V. 1, p. 126, v. 2, p. Ill, and Morse. Shell-mound of Omori, p. 

 27, pi. 18, f. 1.). 



The lieight is a little greater than the length, the surface covered with tine 

 radiating stria3 croEsing the lines of growth. Besides, the species is easily 

 recognized by its crenulated inner margin ami hy its ilat Innula. It is by far 

 more frcKjuent in tlie Tokio-Bay than it was formerly supposed to be, bnt it docs 

 not occur frequently in any of the tertiary deposits, and the specimens, not reach- 

 ing the size of the living ones, are in every respect so much like them tliat there 

 secins to be no necessity for discussing here tlie value of tiio statements of Mores 

 conc<jrning the smaller size and comparatively smaller length of the recent shells. 

 The differences given by Moi-se— viz. 1 to 1.057 as proportion of the length to the 

 height of sliell-mound specimens, and 1 to 1.042 for the same dimensions of the 

 recent ones — are but slight, and so the case may possibly be as in Dosinia exolefci L. 



I'apes dectissatus Linne. 

 (Syst. nat. cd. 12, p. 1135, as Venus. — rjmelin, syst. nat. L. ed. 13, p. 

 3294, no. 35, with variutiiB sub no. 57, 04 and 99, as Venus.— Lamarck, 

 liist. nat. 2d. cd. v. G, p. 375, as Venus.— Forbes and Ilaidey, brit. Moll, 

 pi. 25, f. l,and v. 1. p. 379.-Sowc!rby, Tiie-s. Conch, v. 2, p. G93, pi. 150, 



