382 SHELLS AND SHELL -FISH. PART II. 



Calceola Sw.* Shell ovate ; posterior hinge margin 

 angulated ; one cardinal tooth, and generally a small 

 single lateral tooth in each valve. 



C. angulata Sw. Am. Tr. 1827, pi. 3. f. 1. 



ALASMODON Say- Trigonal ; nearly equilateral ; bosses 

 large, prominent ; two cardinal teeth. 

 A. undulata Say. 



Uniopsis Sw. Oval ; bosses prominent ; cardinal teeth 



two., irregular, receding from the anterior margin. 



U. Mytilo'ides. (Jig. 62. )f 



Margaritana Schum. Elongated, and somewhat ar- 

 cuated ; bosses small ; posterior hinge plate long, 

 convex, sometimes with the rudiments of a tooth j 

 cardinal teeth two or one, small, obtuse. 

 M. elongata Lam.\ arcuata Barnes. 



Complanaria Sw. Shell winged ; the valves connate ; 

 the bosses very small and depressed ; cardinal teeth 

 two or three j lateral teeth represented by irregular 

 grooves, 

 gigas Sw. Sow. Gen. f. 141. rugosa Sw. (Al. rugosa} Barnes. 



FAMILY 2. ARCADE. Arch-Shells. 



Marine ; hinge margin furnished with numerous small 

 well-defined teeth, without any distinction of cardinal 

 arid lateral ; umbones generally remote, mostly covered 

 with an epidermis. 



NUCULA Lam. Perlaceous ; shape various ; beneath the 

 umbones, a spatulate enlargement or pit containing 

 the cartilage ; teeth small, numerous, prominent, and 

 pectinate : marine and fluviatile. (fig. 125. f,g.) 

 margaritacea. Sow. Gen. f. 7. 



* The situation of tliis type seems doubtful, but as I have more than one 

 species of the same form, but without the small lateral tooth, I conjecture 

 they all stand between Alasmodon and Anodon. 



f See note at p. 289. 



% This is the true Mya margaritifera of British authors, for which La- 

 marck only quotes the figures of Pennant and Da Costa; and as he was the 

 first to distinguish it as different from the other European species, I think 

 his specific name has every right of priority. 



