TRANSACTIONS OF WAGNER 

 1 1 7O 



TERTIARY FAUNA OF FLORIDA 



type for more than half a century and was specifically named as such by Gray 

 and Herrmannsen in 1847. Its characters are as follows : 



Gills on each side with only the direct and reflected inner lamina developed ; 

 hepatic glands arborescent, projecting from the ordinary body wall. 



Shell small, more or less transversely ovate, posterior end usually shorter; 

 anterior part of the hinge provided, in the right valve, with a narrow lamina 

 having a minute cardinal hook at the proximal end; the left valve with a 

 similar lamina on which the hook is less prominent or even absent ; external 

 ligament obsolete, amphidetic, leaving no traces on the shell ; resilium strong, 

 internal, posterior, seated on nymphs of which the right one is usually less 

 strong; the ventral surface of the resilium, in the larger species, with a thin 

 calcareous deposit, often wholly absent and never forming a developed litho- 

 desma; the distal portions of the laminae sometimes obsolete. 



Sections : 



I. Montacuta s. s. Type M. substriata Mtg. 

 II. Decipula Jeffreys. Type D. ovata Jeffreys. 



Teeth obsolete in the left valve ; nymphs not developed. 

 III. Orobitella Ball. Type M. floridana Ball. 



Laminae obsolete but cardinal hooks persistent, the sockets of the 

 resilium elevated. 



An examination of the specimens of Decipula ovata in the Jeffreys col- 

 lection shows that they differ from typical Montacuta by the obsolescence 

 of the teeth of the left valve, while the resilium is inserted directly on the 

 shell without the intervention of a nymph. I am unable to decide whether, as 

 Jeffreys supposed, the Tellimya avails of G. O. Sars (Moll. Reg. Arct. Norv., 

 p. 341, pi. 34, figs, la-c, 1878) is the same shell or not, as Professor Sars's 

 figure of the hinge of his shell is quite different from the actual hinge of 

 Jeffreys's specimens. These are from Osterfiord, Norway, and the Fosse de 

 Cap Breton. The great difficulty encountered in getting at the characters of the 

 hinge in these minute shells renders it likely that the differences are due to 

 misinterpretation, and that from its deep-water habitat Decipula has become 

 somewhat degenerate and has been derived from Montacuta, of which it may 

 be regarded as a section. 



Turton originally wrote it, though the form is not in accord with modern methods. It is 

 at any rate in general use, and was probably proposed by Turton from the point of view 

 that Montagu is itself a corrupt derivative from mons and acutus. I find that some 

 members of the Montagu family used the form Montacute as their surname. 



