S T R ^ A. 



Species 12. (Fig. a, h, Mus. Brit.) 



OsTE^EA ANGULAT.4.. Ost. tcstd tngoiid, hrevi, temtius- 

 culd, albidd, strigis jnirpureis paucis invgnlaribus 

 radiatd ; apicilms incvrvis, mbspiralibus ; valvuld 

 superiori depressd, parvd, ad marginem ventralem 

 leviter plicatd ; inferiori profundd ad apiceni arcua- 

 tim productd, ad marginem ventralem leviter plicatd, 

 expansd, valvam inferiorem longe siiperante ; car- 

 dine tenui. 



Thk angular Ostr^a. Shell trigonal, short, rather 

 thin, whitish, rayed with few, irregular, purple 

 streaks ; apices incurved, subspinal ; upper valve 

 depressed, small, slightly plicated at the ventral 

 margin ; lower valve deep, produced in an arch at 

 the apex, slightly plicated at the venti-al maririn, 

 expanded, far exceeding the lower valve ; hinge 

 thin. 



Lamarck {Gnjphmi arujulata). Anim. s. vert. Grypha^a, 

 sp. 1. 



n„b. ? 



The great peculiarity of this shell is the depth of the 

 lower valve under the hinge, above wliich the apex 

 curves upwards and sjiirally. 



Species 13. (Mus. Brit.) 



OsTR^A sp.WHULATA. Ost. testd magnd, compressd, sub- 

 quadratd, solidd, valvuld inferiori planulatd, mar- 



ginibus albis perfoliaceis ; margine dorsali lato ■ 

 valvuld sujjerioii aureo-fulvescenti, concentrice lineis 

 i-vbescentibus pictd, prope margines laxe squamatd, 

 late, expansd; cardine lato subplanulato ; intuf 

 partim subviolaced, marginibus denticulatis. 



The si'ATiiULATE OsTR^A. Shell large, compressed, 

 subquadrate, solid, lower valve flattened, with 

 white very foliaceous borders ; dorsal margin 

 wide ; upper valve golden-brown, painted concen- 

 trically with reddish lines, loosely scaly towards 

 the margins ; a little violet in parts within, with 

 denticulate borders. 



Lamarck. Anim. s. vert. Ost., No. 16. 



Bab. Guacomayo, Co. of America. 



It is not possible to speak with certainty respecting 

 this species, which may quite possibly be a very aber- 

 rant variety of 0. prismatica. I am led to assign 

 Lamarck's name and description, however vague, to the 

 shell, because that author remarks that his species 

 approaches the preceding one, the 0. denticulata of 

 Born, which our shell unquestionably does, differing, 

 however, in the flat and spathulate form. It might, 

 perhaps, be feasible to link together 0. denticulata, 

 0. spathiilata, and 0. iridescens, under the first of the 

 three names ; but the worn state of the ponderous and 

 richly coloured specimens of the third which we have 

 hitherto met with, prevents a decisive conclusion on the 

 subject. 



January, 1871. 



