382 



SHELLS AXD SHELL -FISH. PART IT. 



Calceola Sw.* Shell ovate ; posterior hinge margin 

 angulated ; one cardinal tooth, and generally a small 

 single lateral tooth in each valve. 



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



Alasmodon Say. Trigonal ; nearly equilateral ; bosses 

 large, prominent ; two cardinal teeth. 

 A. undulata Say. 



Uniopsifi Sw. Oval ; bosses prominent ; cardinal teeth 

 two, irregular, receding from the anterior margin. 

 U. Mytiloides. (Jig. 62. )f 



Margaritana Schum. Elongated, and somewhat ar- 

 cuated ', bosses small ; posterior hinge plate long, 

 convex, sometimes with the rudiments of a tooth ; 

 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 ; 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 

 and 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. (fg. 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 Anodo?i. 



t See note at p. 28a 



X This is the true ^fl/a marf^aritifcra of British'authors, for which La- 

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

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

 his specific name has every right of priority. 



