308 DONAX. 



radiata, postice biangulata, antice producta, obtusa, margine 

 ventrali convexa. — Of an oblong form and solid substance, with 

 an obtuse second angle and produced margin. 



19. Cayennensis (f. 46, 47, 48), Lamlc. — Testa subventrieosa, 

 tenuiuscula, radiatim striata, postice prope anguluin undulatim 

 decussata, colore luteo-purpurascente, seu rosea, seu purpurea, 

 prope umbones albo-radiata; latere antico oblongo ad tenninum 

 rotundo, latere postico brevi, angulo obtuso, area postangulari 

 lata, granoso-striata, margine medio dentato, margine ventrali 

 parum convexo, postice valide dentato, valva dextra sinistral!) 

 superante. — Of an oblong form, granulated and decussated near 

 the obtuse posterior angle and on the area behind it. The ven- 

 tral margin of the right valve appears a little beyond that of 

 the left, showiug the strong dentition at the posterior side. 



20. cuetus (f. 20), Sowh. — Testa D. Ccu/ennensi simili, sed 

 longe magis abbreviate. — The abbreviated form of this shell is so 

 constant through all the varieties of colouring that after examining 

 a number of our own specimens with Mr. Taylor's we have no 

 hesitation in distinguishing it. 



21. RtjGOsus (f. 27, 28, 29), Linn. — Testa elongata, tumida, 

 crassa, luteo-purpurascente, seu aurantio-rosea, seu late fasciata, 

 latere antico subacuminato, prope marginem lcevi, medio et. postice 

 radiatim striata, latere postico brevissimo, undulatim rugato, striis 

 radian tibusdecussato,angulosubcarinato, area postangulari convexa. 

 ■ — Of an elongated form and rugosely decussated behind the angle. 



22. elongatus (f. 12), Lamlc. — Testa D. rngosce simili sed 

 magis acuta, angulo acute carinato, striis radiantibus magis dis- 

 tantibus, margine valide denticulato, area postangulari fortissime 

 rugato et dentato. — The angle more keeled, all the sculpture 

 more coarse than D. rugosa, the margin very strongly denticulated. 



23. obesvlus (f. 15), Des/t. — Testa brevi, solida, pallida, intus 

 purpurea, antice laevigata, acuminata, postice tenuiter striata, 

 carinato-angulata, brevissima, area postangulari lata, subrecta, 

 concava, ininutissime granulata. — Of the short wedge form, with 

 th» posterior area finely granulated. 



24. denticulatus (f. 33, 34, 35, 36), Linn. — -Testa brevi, tri- 

 gona, solida, sulcato-striata, albii, aurantia, purpurascente seu 

 coloribus variis radiatim picta, antice acuminata, postice biangu- 

 lata, area postangulari angusta, concentrice rugata, area, inter 

 angulos radiatim sulcata, marginibus dentatis. — A short triangular 

 species, variously painted, with a double angle. Between t lie 



