JUKES-BEOWNE : CRETACEOUS AND EOCENE VENEEIDiE. 163. 



has convex valves (not compressed), and no defined escutcheon nor 

 sunken ligament. 



On the other hand, C. circularis, Desh., and C. pusiUa, Desh., seem 

 referable to the subgenus Gouldia, as exemplified in our recent 

 G. minima. Oouldia differs from other sections of the genus in the wide 

 divergence of the teeth, the anterior cardinal of the right valve sloping 

 forward so as to point to the middle of the anterior lateral pit; another 

 peculiarity is the union of the anterior adductor and the pedal scars, 

 which in all other forms of Circe are separate from one another. 

 In specimens of C. pusilla with which M. Cossmann has kindly 

 supplied me, the pedal scar does seem to merge into that of the 

 adductor ; the shell is so minute that it is difficult to be sure, but 

 I cannot see any separate scar. The teeth are certainly those of 

 Goiddia. 



Another species of Circe was afterwards described by M. Cossmann 

 under the name of C. Dumasi, from the Middle Eocene of Bois Gouet 

 in the Loire Inferieure,' and as he has also been kind enough to send 

 me specimens of this I am able to say that it undoubtedly belongs to 

 Circenita, and that it possesses the small round separate pedal scar 

 which characterizes all members of the genus except Gouldia. 



10. Ptychomya, Agassiz. 



This shell has been referred to different families by different authors. 

 By Agassiz (1842) it was classed near Mya; by d'Orbigny (1844) it 

 was described as a CrassateUa ; and it was referred to the same family 

 both by Pictet and Campiche (1866) and by Stoliczka (1871); but 

 Dames in 1873 gave reasons for regarding it as nearly related to the 

 recent Crista (a subgenus of Circe). Fischer (1887) seems to have 

 concurred in this view, but was evidently doubtful about the existence 

 of an anterior pit in the right valve, and so far as I can ascertain no 

 one has yet seen the hinge of a left valve. 



By the kindness of Mr. Woods I have been able to examine the 

 specimen from which his figure of the hinge of the right valve was 

 drawn. ^ As might be inferred from the figure, it is not clear from 

 this specimen that there were really three cardinal teeth ; only two of 

 them are quite distinct, these being a small anterior and a thick 

 median ; a posterior tooth may have been present, but, if so, it was 

 fused with the nymph and has been broken off, all that remains being 

 a broad flat plate below the deeply inset trough which held the 

 ligament. The anterior portion of the shell is also broken, but 

 enough remains to show that the area in front of the cardinals was 

 small and tliat the border of the hinge-plate ran nearly stx'aight to the 

 anterior side, forming a ridge with a small hollow or trough above it. 

 This may have received an anterior lateral tooth, if one existed in the 

 left valve. 



The shell agrees with Crista in being very thick, in bearing strong 



1 Bull. Soc. Sci. Nat. de I'Ouest. 



^ " Cretaceous Laraellibranchia " : Pal. Soc. Mon., vol. ii, pi. xxvii, ligs. 24-6, 



