20 TEREBRATULID^E. 



mostly blunt and often worn by attrition, never much pro- 

 duced : foramen triangular, occupying nearly the whole of the 

 dorsal area : deltidium exceedingly slight : hinge-plate thick 

 and broad: teeth strong and triangular : sockets broad but not 

 deep : skeleton consisting of two very slight and narrow riband- 

 like plates or ribs, placed as in A. decollata, but having only 

 their front edges free, the remaining portion being united with 

 the shell; within the upper valve is a septum, extending from 

 the centre of the hinge to nearly the front margin, besides a 

 few parallel but indistinct striae ; the lower valve has a strong 

 blunt central ridge, which is higher in front and occupies about 

 half of the interior ; the front margin is minutely crenulated 

 inside. L. 0-06. B. 0-075. 



HABITAT : East Shetland, Skye, and co. Antrim ; 

 Moray Firth (Dawson) ; Dublin Bay (Waller) ; Exmouth 

 (Barlee and Clark) ; Guernsey (Lukis & J. G. J.). Fos- 

 sil in the Coralline Crag. Sars has found it at Chris- 

 tiansund, Bergen, and Manger in Norway ; I have taken 

 it on the Normandy coast ; and among some small shells 

 which I received through M. Verany from Sardinia was 

 a single valve of this species. 



The animal closely resembles that of A. decollata. 

 The anterior occlusor or retractor muscles are of enor- 

 mous size, and their impressions on old shells are very 

 conspicuous and deep, somewhat resembling those of 

 Crania. Very young shells have scarcely any of the 

 tubular perforations ; and their beaks remind one of 

 the bill of a Platypus. These delicate processes become 

 afterwards hardened and blunted by contact with the 

 external world, like the exquisitely sensitive feelings of a 

 child. The fry may be occasionally seen attached to the 

 outer folds of the mantle. They appear to be kidney- 

 shaped, and are of different sizes, or degrees of deve- 

 lopment. 



This species was named, but not described, by Mr. 

 S. Wood in 1840 as a tertiary fossil ; and I was fortu- 



