192 CRETACEOUS PELECYPODA 



most anterior is sub-trigonal, attenuating towards the front ; a low ridge runs from 

 the top of this anterior to the base of the middle cardinal, dividing obliquely the 

 great gape between them in two pits into which the superimposed anterior cardinal 

 teeth of the right valve fit. 



This explanation of the relative position of the hinge-teeth readily shows the 

 great similarity existing between the present genus and Veniella as already 

 indicated. 



Only one recent species, Ci/p. islandica, is known ; typical forms occur in the 

 tertiary and cretaceous beds ; but whether any of the Jurassic and older Ci/pr'mce 

 really belong to this genus has yet to be satisfactorily ascertained. 



I'l'rt. Cicatrea, StoL, 1870. I propose this name provisionally only as a 

 sub-division of Ci/prina, taking our cretaceous species Q/p. [Cic] corcUalis as the 

 type. The form of the shell is distinguished by its remarkably sharp and high ridge 

 running from the umbones to the postero-inferior end of the shell ; the beaks are 

 distant and strongly incurved, and from each runs posteriorly a rather short but 

 deeply bifurcate groove in which the ligament is lodged. This very much recalls 

 some species of Splsula, for there are no special fulcra ; the hinge margin below 

 the beaks is entire. The posterior cardinal teeth are rather narrow in both valves 

 (while in Cyprina proper the one in the right valve is very thick and bifurcate) ; 

 the two anterior cardinals in the left valve are very large, the same superimposed 

 teeth in the right valve, however, very small ; the anterior muscular impression 

 is anteriorly margined by a sharj:* ridge. The form of the shell strongly recalls 

 HemicarcUum. 



The principal peculiarity of this perhaps new generic form is the presence 

 of a deep bifid ligament groove and the relative proportions of the cardinal teeth ; it 

 remains to be shown by further discoveries whether these characters are connected 

 with the remarkable cordate and elongated form of the shell, and whether they are 

 in other forms constant. A species that likely belongs to it is d'Orbigny's 

 cretaceous Isocardia p)yi'cnaica. 



15. C'l/prinopsis, Conrad, 1869, (Am. Joui'n. Conch., v, p. 101,) is charac- 

 terized as " equivalve, two anterior cardinal teeth and one very oblique tooth in 

 the right valve, pallial line entire ;" type Artemis elliptica, Smith. Journ. Geolo- 

 gical Society, vii, p. 15, figs. 2-3. I do not know the species unless it is believed 

 to be identical with Meretrix ovcdis, Gabb, (Pal. Calif., i,) which does not seem to 

 exhibit any particular distinctions from Cytherea. 



Cretaceous species belonging to the Glossw.-e, 

 Pictet and Campiche in their Pal. Suisse (4""= ser., 3"" pt., p. 211, &c.,) note the species 

 referable to this family under the generic names of Cyprina, Ci/pricardia, Veriilia, and Isocardia. 

 I am' only sorry to say that it is almost impossible to comment upon most of the species described, 

 their hinges being known comparatively only in very few instances ; however the review will show us 

 bow much remains to be done for the study of the family. 



As it appears of little consequence in which order the species are here enumerated, I shall 

 follow the arrangement of Pictet and Campiche, in order to facilitate comparison, adding in each 

 ease the species which were described under the abovcmcntioned generic names. 



