50 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



bles that of the Radiohte in having two prominent teeth in the upper 

 valve ; but they are curved, so as to admit of obhque movement. 



Figs. 17 & 18. — Lateral views of the internal mould of Caprotina 



quadripartita, B'Orb. Reduced |-. From a specimen collected 

 by Mr. Pratt. 



Fig. 17. Fig. 18. 



u, u, left umbo ; r, r, right umbo ; /, ligamental inflection ; c, c, cartilage ; 

 t, t, f, t', dental sockets ; a, a', position of adductor muscles ; e, portion 

 of the third lobe is here broken away. (The first and fourth lobes, those 

 on each side of the ligamental inflection, appear to be the two divisions 

 of a great internal cartilage like that of the Radiolite, figs. 15, 16, c, c.) 



Each tooth is supported by a plate, to which the shell-muscles were 

 attached. The umbonal cavity of the upper valve is divided by a 

 vertical plate (as in Radiolites polyconilites), so that moulds of 

 the interior are four-lobed, two of the lobes representing the cartilage, 

 and two the divided umbo. 



A similar plate divides the interior of the upper (or spiral) valve 

 in Caprina and Caprinella. In each case it supports the anterior 

 hinge-tooth, but so obliquely that the posterior cavity (or lobe) is 

 much the smaller. The interior of the lower valve is divided into 

 two very unequal cavities by an oblique plate, answering apparently 

 to the muscular inflection of Hippurites and Diceras. The liga- 

 mental cavity in the lower valve of Capi'otina is subdivided into 

 numerous unequal pits. 



Some species of Caprotina are long and straight, with small flat 

 opercular valves, like miniature Radiolites ; they occur in groups, 

 frequently attached to Oyster-shells. 



Caprina. — In Caprina (figs. 21, 22) the fixed valve has the 

 same structure as in Caprotina, whilst the upper is perforated by 

 canals ; another proof of the subordinate importance of shell-struc- 

 ture. These canals are simple tubes, extending from the umbo to 



Norf.pl. 5. fig. 22 {= Caprotina, Morris, "Catalogue," 1st edit., Caprina Rus- 

 siensis, D'Orb. 1845, Caprotina Russiensis, D'Orb. 1850, and Chama cornucopice, 

 D'Orb. 1847), is undoubtedly a Chama. 



