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TEREfiRATULA. 



the same substance as the shell), which are sometimes 

 short, simple, and recurved, hut sometimes of considera- 

 ble length, branched and variously bent, and generally 

 anastomosing: these generally commence on each side of 

 the hinge, but sometimes near the centre of the shell, and 

 they are sometimes united to the shell at other points. 

 What purpose these appendages answer we cannot pre- 

 tend to say ; Lamarck thinks they are supports to the 

 animal within. Muscular impressions, two in each valve, 

 sometimes very strong, but mostly very indistinct ; those 

 in the perforated valve oblong, central and close toge- 

 ther; those in the other valve rather triangular, with 

 rounded angles, nearly central, but rather more distant. 



Terebratula is distinguished from Anomia by its regu- 

 larity, its produced beak, its being attached by means of 

 a fibrous pedicle, and its internal appendages : it will not 

 be confounded with Crania, Thecidea, or Hipponyx, be- 

 cause they are all attached by the outside of the shell : 

 the very peculiar though regular form of Calceola will 

 prevent its being mistaken for that. Orbicula and Lin- 

 gula have no hinge teeth, which circumstance is a suffi- 

 ciently discriminating mark. 



The recent species of this Genus are found attached 

 to stones and to each other in the ocean, in all cli- 

 mates; but only two or three species are found on our 

 own coasts. They are not, in general, remarkable for 

 the brilliancy of their tints, though a few of them are 

 very prettily coloured; but they are mostly of a dull 

 horn colour. Many of them are variously and longi- 

 tudinally striated and grooved, and dentated at their 

 edges; some are remarkable for a deeply emarginate 

 superior edge to one valve, and a corresponding promi- 

 nent edge to the other: others, again, have one side 

 entirely depressed, and the other elevated ; and many are 

 very smooth on the outside, as well as somewhat hyaline. 

 They are rather highly valued by collectors, especially 

 when highly coloured. 



The fossil species are much more numerous than the 

 recent; they occur in all the secondary and tertiary for- 

 mations, except those of fresh water origin, and we never 

 met with any of them in the upper marine formation J* 

 I^articular species are peculiar to certain beds, which, 



