AVICULID^. 2 19 



Hemisplierical pearls have been found developed fi'om their 

 inner surface, and spherical pearls of the same prismatic-cellular 

 structure occur detached, in the chalk. — Wetherell. The Ino- 

 cerami of the gault are nacreous. 



CATiLLUS, Brongniart, 1822. (Haploscapha, Conr.) Shell 

 flattened or ventricose, elongated, cordiform or suborbicular, 

 subequivalve, inequilateral; hinge-line nearly straight, its margin 

 with a short series of small cavities, gradually enlarging ; shell 

 fibrous, /. Lamarckii^ Brongn. (cxxx, 56). Cretaceous. 



ACTiNOCERAMUS, Meek, 1864. Proposed for a small group of 

 Inocerami of the type of /. sulcatus, Park, (cxxx, 57). They have 

 a rather short and sometimes oblique hinge-line, the left valve 

 is often slightly more globose than the right, and both are dis- 

 tinguished from other similar forms by the presence of radiating 

 ribs. The fibrous layer appears to be often thinner in Actino- 

 ceramus than in most of the concentrically sulcated Inocerami. 



YOLYiCERAMUS, StoHczka. Type, I. involutus, Sow. (cxxx, 58 ', 

 which has the left valve strongly involute like a nautilus or 

 somewhat resembling a Gryphsea, while the right valve is verj'' 

 much smaller, flattened, slightly tumid at the apex, resembling 

 an opei'culum ; the hinge-line is curved, conformed to the ovately 

 rounded aperture of the left valve, thickened and provided with 

 numerous ligamental pits, as in other typical species of the 

 genus. 



Anop^a, Eichwald, 1861. 



Distr. — 3 sp. Cretaceous ; Russia. 



Equivalve, inequilateral, elongated, with the shorter anterior 

 part narrower, beaks close together, with a deep circumscribed 

 lunule in front of them ; ligament situated in a number of 

 roundish pits in the straight cardinal margin, which has a rib- 

 like tooth in the left valve below the beak, extending anteriorly 

 for a short distance. Principally^ differs from Inoceraraus by 

 the presence of a deep lunule and by the internal hinge-rib (in 

 the left valve). 



Gervillia, Defrance. 



Etym. — Dedicated to M. Gerville, a French naturalist. 



Distr. — Fossil, 37 sp. Carb. — Chalk ; Europe. G. anceps, 

 Desh. (cxxxii, 90). 



Shell like Avicula ; elongated ; anterior ear small, posterior 

 wing-like ; area long and flat, cartilage-pits several, wide apart ; 

 hinge-teeth obscure, diverging posteriorly. 



BAKEWELLiA, King. Shell small, inequivalve, caitilage-pits 

 2-5 ; hinge with anterior and posterior teeth ; anterior muscular 

 impression and pallial line distinct. Fossil, 5 sp. Permian ; 

 Britain, Germany, Russia, U. S. G.antiqua, Munst.(cxxx,59,60). 



