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end of its cartilage, which runs through the beak of the shell, whilst the 

 other end might be connected with this apparatus, the resiliency would 

 be increased, and the danger lessened of the cartilage, or of the animal 

 itself being injured by those shocks which it might receive whilst thus 

 suspended. 



The following are species of this genus which are not, I believe, gene- 

 rally known. 



Terebratulites coarctatus. A nearly heptagonal shell, set with beaded 

 longitudinal ridges : the larger valve sulcated, with its sides appearing as 

 if pinched together, and terminating at the beak with a large foramen ; 

 the hinge small, close, and curved ; and the smaller valve convex. 

 Plate XVI. Fig. 5. 



T. triquetrus. A three-cornered shell : the anterior and posterior sides 

 compressed ; the superior margin more rounded, but dented in the mid- 

 dle : both valves convex, and terminating in a point, with a close and 

 curved hinge ; the large valve having a narrow groove, commencing in 

 nearly the centre, and extending to an umbilical-formed depression in 

 its lower part, just before the beak turns, and finishes with a round 

 foramen. 



Two different specimens, both appearing to belong to this species, are 

 figured Plate XVI. Fig. 4 and 8. In the former, a small portion of the 

 shell still adheres on the lower part of the larger valve, which is here 

 shown uppermost; but the latter specimen, which is here shown with 

 the smaller valve uppermost, has none of the shell remaining. The sub- 

 stance of these fossils is a very fine close-grained lime-stone. I am unac- 

 quainted with the habitats of these, or of the former fossil. 



The casts of some species of Terebratulae are of a most extraor- 

 dinary form, and obtained a considerable degree of attention from the 

 early oryctologists. It appears that these casts were first noticed by Pliny 

 (Lib. xxxvii. Cap. 57), who describes certain stones, some of which were 

 white and others brown; the former bearing, in their figures, some 

 resemblance to the male, and the latter to the female, parts of gene- 



