DONAX. 313 



50. obscukus (f. Ill), Reeve. — Testa D. nueuloidi simili sed 

 conceutrice striata. — -Without re-examination of the two shells, 

 for the present locked up in the late .Mr. Cuming's cabinet, I 

 cannot decide whether this is uot a variety of D. nuculoides. 

 The rpiestion would depend upon the character of the described 

 striation. 



51. serra (f. 87), Chemn, — Testa crassa, ovato-subtrigonii, 

 lata, carnea purpurascenti, laevigata, antice rotundatim oblonga, 

 margine ventrali concavo, intus crenato, postice subcontractor 

 angulo postico obtusissiino, rugis denticulatis serrato, area post- 

 angulari concava, umbonibus obtusis. — A thick, oval shell, very 

 obtuse at the. extremities and angles, and serrated at and behind 

 the angle by denticulated ridges. 



52. trunculus (f. 5S, 59, GO), Linn. — Testa elongato-sub- 

 trigona, compressa, solida, laevigata, obscure radiatim striata, 

 alba vel purpurascente, fulvo sen purpureo fasciata, antice elongatu, 

 lata, rotundala, conceutrice leviter rugata, postice brevi, convexa ; 

 margine ventrali medio convexo, postice subcontfacto, intus deu- 

 ticulato, valva dextra alteram superante, margine dorsali declivi, 

 recto, concavo, valva sinistra peculiariter elevata et compressa. — 

 The variation in form is considerable among the specimens of this 

 species, some being flatter, broader, and more truncated than 

 others. There is a peculiarity in this and the following species 

 which has not been noticed. The right valve overlaps the other 

 at the posterior part of the ventral margin, while the left valve 

 is peculiarly flattened and elevated above the other at the dorsal 

 line near the hinge. Several true British specimens exist : one 

 well authenticated, in Mr. Jeffreys' collection. 



53. vellicatus (f. 61, 62, 63), Reeve. — Testa polita, tumida, 

 obscurissime striata, truueata, liliaceo radiata, valvis supra et infra 

 parum insequalibus, latere antico producto, rotundo, latere postico 

 truncato, margine ventrali postice subcontract, area postangulari 

 brevi, concava. — The contraction of the ventral margin near the 

 posterior angle, whence this shell derives its name, is a variation 

 common to many species. The curious inequality of the valves 

 at the two margins observed in the last is shown in a less degree 

 in this. 



54. vittatus (f. 66, 67, var. semistriata, i. 70), Da Costa. — 

 Testa ovali, gibbosa, solida, luteal, fulvo late radiata, purpureo fas- 

 ciata, antice polita, medio et postice minute radiatim striata, ad angu- 

 luin et ante usque ad medium lineis impressis punctatis subconcen- 



