619 



23. Cythek^a Dolabella (pi. cxxvii. f. 15), 8otoerhy,jun. 



Cyth. testa trigonu, solida, alta, pallida, laevigata, epidermide 

 fusca induta ; latere postico angulato, subexcavato, ad basin sub- 

 rostrato ; latere antico rotundato ; lunula parva, distincta ; mar- 

 gine ventrali subarcuato ; umbonibus acutis, 



A pale trigonal shell, with a dark brown epidermis ; the ventral 

 margin and lower part of the anterior side rounded, the posterior 

 angle prominent and acute. 



Red Sea. Mus. Cuming. 



24. Cyther^a meretrix (pi. cxxix. f. 48, 49, 50), Linn. 

 Syst. Nat. LamarcJc, Anim. s. vert. Ci/th. no. 6, 



Cyth. testa ponderosa, ovali-subtrigona, laevi, alba, postice 

 cserulea, prope umbones vel omuino angulatim fusco-maculato ; 

 margine ventrali subiuflato; latere postico vix angulato, sub- 

 elongato, ad terminum subacuto ; lunula magna, indistincta ; liga- 

 mento magno. 



Lamarck has separated this and the following member of the 

 same group upon the mere ground of variations in colour. I 

 am inclined to think that such distinctions are untenable, and am 

 almost persuaded that this species and the eight following might 

 be united under one name, seeing that they pass imperceptibly 

 into each other, and that in a young state it is almost impossible 

 to distinguish them. As, however, such extensive recombinations 

 would hardly be consistent with the usual course of nomenclature, 

 I have endeavoured, from a number of specimens, to arrange a 

 series of variations in form, and have applied to them the same 

 names w^hich Lamarck attached to variations in colour. This species 

 has an oval form, rather lengthened and angular at the posterior 

 side, while the ventral edge is rounded. It is generally white, 

 with a broad purplish posterior area, and a few angular markings 

 near the umbones, or, as in fig. 5, nearly all over the shell. The 

 latter is in Mr. Cuming^s collection, and is from China. 



25. Cyther^a petechialis (pi. cxxix. f. 51, 52), Lamarck, 

 Anim. s. vert. Cvth. no. 2. Var. C. grapliica, Lamarck, no. 7. 



Cyth. testa C. meretrici simillima, sed multum altiore ; margine 

 rotundissimo ; latere postico rotundatim angulato ; colore sub- 

 griseo, fusco-rufescente angulatim liueato. 



Shell rounder and higher than C. meretrix ; the ventral margin 

 very much rounded ; the lateral angle rather more distinct ; co- 

 loured in the same way as C. meretrix, but without the purple 

 dosterior area. 



