42 ANATINIDJE. 



rib indistinct : J dnge-line obtusely angular : hinge-plate thick 

 and strong: ossicle semilunar, slightly attached, and conse- 

 quently often lost in dead specimens: inside creamcolour, some- 

 what glossy and nacreous ; edges blunt : scars large and well 

 denned. L. 0-6. B. 0-8. 



Yar. truncata. Shell oblong ; front margin straight ; pos- 

 terior margin abruptly truncated. Anatina truncata, Turton, 

 Dith. p. 46, t. 4. f. 6. 



HABITAT : From Guernsey to Unst, in crevices of 

 rocks and old oyster-shells, between 5 and 35 f., as well 

 as occasionally buried in tufts of Corallina officinalis at 

 low water ; local, but widely diffused. The variety is 

 from Exmouth, Tenby, and Cork. Fossil in the Coral- 

 line Crag (S. Wood); Palermo (Philippi). Foreign 

 range : Finmark to the Cattegat, 3-40 f. (Loven and 

 others) ; north of France (De Gerville and others) ; 

 Provence (Martin) ; Algeria (Deshayes and Weinkauff) . 



This is the smallest British Thracia ; and its habitat 

 is different from that of its congeners. It may also be 

 known by its irregularly oval shape, its less angular 

 outline, uniform granulation, and comparatively large 

 cartilage-pit. The young are triangular, and somewhat 

 resemble a Montacuta. A full-grown specimen taken 

 from a narrow chink in a piece of limestone well exem- 

 plifies the mode in which shells are constructed. Part 

 of the left valve had been crushed, apparently by acci- 

 dental pressure ; and in order to repair the damage, an 

 inner layer was formed by exudation from the mantle, 

 to which the broken fragments were cemented and still 

 adhere. The distorted growth of this species shows 

 that it does not excavate the holes in which it lives. 

 It sometimes appropriates the labours of other animals, 

 but never unjustly or consciously, like a plagiarist. 

 The original and short-lived fabricators of the dwellings 

 subsequently occupied by the Thracia are beyond the 



