CEASSINA. CONCHIFERA. 101 



SECTION III. TENUIPEDES. 



FAMILY I. NYMPHACEA. 



Two primary teeth at most in the same valve ; shell often 

 slightly gaping at the lateral extremities ; ligament exterior ; 

 umbones generally projecting outwards. 



In this group Lamarck assembles different shells, which were referred by former 

 naturalists to the Solens and Tellinee, but which possessed not wholly the characters 

 of either. The foot of the animal is small, and often compressed, the primary teeth 

 rarely diverging, and never more than two in each valve. The species are all littoral. 



1 . Destitute of lateral teeth. 

 Gen. 26. CRASSINA, Lam. Venus, Mont. 

 Shell suborbicular, transverse, equivalve, close ; hinge with two 

 strong diverging teeth in the right valve, and two very une- 

 qual ones in the left ; ligament exterior. 



C. Danmoniensis, Lam. Shell rounded,, trigonal, fulvous brown, 

 with distant, regular, strong transverse ribs, and the margin cre- 

 nated. 1 inch long. Inhabits British coasts. B. Brown's II- 

 lust. pi. 18, fig. 1. 



Gen. 27. CAPSA, Lam. Donax, Lin. 



Shell transverse, equivalve, close ; hinge with two teeth in the 

 right valve, and a single bifid one in the other ; ligament 

 exterior. 



C. Icevigata, Lam. Shell triangular, subequilateral, obsoletely stri- 

 ated ; epidermis greenish-yellow within, and violet at the umbo. 

 2 inches long. Indian Ocean Chem. vi. pi. 25, fig. 249. 



C. castanea, Turton. (Donax, Mont.) Shell strong, transversely 

 oblong, with a few obsolete concentric ridges ; colour chestnut, 

 with a deeper coloured curved band. ^ inch long, ^ broad. In- 

 habits Southern coasts of England. Mont. Test. pi. 17, fig, 2. 



2. With one or two lateral teeth. Tellinaires, Lam. 



Gen. 28. DONAX, Lam. Lin. 



Shell transverse, equivalve, inequilateral, with the anterior side 

 very short and very obtuse; two primary teeth in one or 

 both valves, and one or two lateral teeth, more or less sepa- 

 rated ; ligament exterior, short, at the posterior depression. 



This genus are recognized in general at first sight by their particular wedge- 

 shaped or triangular form, and their anterior side shortened and truncated. The 

 ligament in this genus and the Tellince, contrary to what occurs in the genus Ve. 

 nuS) is always on the shortest side of the shells. The animal has two long and slen- 

 der tubes or syphons, and the foot is broad. 



* Margin of the valves entire. 



D. scortum, Lin. Shell triangular, with decussated elevated striae, 

 and the anterior slope flattish ; colour grayish white, with dark- 

 er transverse bands towards the margin ; inside violet near the 

 hinge. 1^ inch long, and 2^ inches broad. Inhabits Indian seas. 

 Lister, pi. 377, fig. 220. 



D. pubescens, Lin. Shell triangular, with decussated striae ; ante- 



