ATTACHED. 77 



having but two cardinal teeth. Astarte differs from Crassatella 

 in having no internal cartilage in the hinge. Some of the 

 species are British, others are from America, and one from Sicily. 

 The fossils occur in Crag, Lower Oolite, &c. A. Danmoniensis. 

 PL V. fig. 110. 



ASTEOLEPAS. Klein, Coeonula Testudinaria, Auct. Che- 

 LONOBiA, Leach. Pig. 15. 



ATLANTA. Lesueur. Fam. Pteropoda, Lam. and Bl. — Deser. 

 Spiral, convolute, transparent, fragile, compressed, with a broad, 

 fimbriated, dorsal keel, and a narrow aperture. This shell, 

 which is called " eorne d'ammon vivant," is found in the 

 Atlantic. The small Pteropod, figured in Sowerby's Grenera as 

 Limacina, belongs to this genus. Atlanta Helicialis, PI. xii. 

 fig. 220. 



ATLAS. Lesueur. A genus of Bullidse without any shell. 



ATEACTODON. Charlesworth. (Mag. IS'at. Hist. 2nd series, 

 vol. i, p. 218,) A genus proposed for the admission of a singular 

 fossil-shell, found on the beach at Pelix-stone, of which the 

 following are the characters : — fusiform, aperture equalling the 

 spire in length, terminating anteriorly in a slightly recurved 

 canal ; columellar lip smooth, curved, thickened posteriorly into 

 a blunt tooth ; spire obtuse.— Obs. This shell would be a Pusus 



. were it not for the tooth on the posterior extremity of the colu- 

 mellar lip. The only species known is regularly striated in a 

 spiral direction, and named A. elegans. 



ATETPA. Dalman, A genus of brachipodous bivalves, dis- 

 tinguished by the valves being nearly equal, and the umbones 

 not separated by an intermediate area. A. reticulata, PL xi. 

 fig. 302. 



ATTACHED. Shells are attached to marine substances by various 

 means; in some cases by a byssus, or a bunch of tendinous fibres 

 passing through an opening between the valves, which gape at 

 their margins to admit a free passage, as in the genera Bysso- 

 arca and Mytilus. In other cases the byssus is of a more com- 

 pact substance, and passes through a perforation in the shell 

 itself. This is the case with many of the brachiopodous shells, in 



