INVERTEBRATE E*AL2EONTOLOGY. 131 



3. CYCLAS, II. and A. Adams (not Brug.). 



Shell orbicular, thin, rather compressed ; hinge with cardinal and 

 lateral teeth present, hut small; surface obliquely or divaricately 

 striated. — Lucina divaricata, Linn. 



4. milthba, H. and A. Adams. 



Shell inequivalve, nearly smooth, or more or less distinctly 

 marked with radiating striae or costas; hinge with lateral teeth gen- 

 erally obsolete. — Lucina Childreni, Gray. 



Mr. Gabb has proposed another subgenus, Here, for his L. Richthorfeani, 

 *from the Cretaceous of California, based on its extremely profound lunule. 

 As this species, however, agrees well in all of its other characters with 

 typical forms of Lucina, and some existing, as well as other fossil species, 

 agreeing equally well with other allied sections, also show this character, it 

 seems scarcely desirable to separate this as the type of a distinct subgenus. 



By some conchologists, Loripes of Poli, 1791, is also included as a sub- 

 genus under Lucina, and it must be admitted that the species they thus 

 range cannot be separated from this genus upon any very distinctly-marked 

 characters of the shell alone. If Poli did not, as suggested by Deshayes,* 

 however, confound a tellinoid with a lucinoid species, when he figured the 

 animal of his typical Loripes with a long siphonal tube, it must differ widely 

 in this character from Lucina, or even from all other types of the Lucinxdce. 

 Until this question can be settled, it seems more proper to view Loripes as a 

 distinct genus. 



Codakia, Scopoli, 1777, is also included by H. and A. Adams, Dr. Stoliczka, 

 and others, as another subgenus, under Lucina. The remarkable difference 

 presented by the comparatively very short foot of the typical species of this 

 group (L. tigerina), as shown by Deshayes (Jour. Conch. Paris, I, 3e. ser, pi. 

 xiv, fig. 3f), together with the strongly radiately costate character of the shell, 

 and its concealed ligament, seem to be sufficiently well-marked peculiarities 

 to separate this type genetically. 



Dr. Stoliczka likewise includes, as a subgenus of the group under consid- 

 eration, Lirodiscus, Conrad, founded on the Eocene Astarte teUinoides, Con. 



* Supp. Coq. Fossilea Environs de Paris, I, 589. 



t At tlie time Deshayes published the paper here alluded to, he did not think the difference between 

 the animal of the type of Codakia aud that of Lucina even of subgeneric importance. In his later pub- 

 lications, however, he admits it doubtfully as a distinct geuus (Supp. Coq. Foss. Envirous de Paris, 

 590). 



