50 nucuuda:. 



both the front dorsal region and the luuular area are manifestly 

 though faintly and minutely marked with divergent strife. Ex- 

 tremity of the produced anterior side rounded, its slope moderate. 

 Posterior side excessively short, not angulated below, but cut off, 

 as it were, in an oblique curve, by the much arcuated ventral 

 margin, which rises behind and is linely crenulated within. Lu- 

 nular area undefined, rather prominent. 



1-5. N. DECLivis, Eimh, f. 147. — "T. parva, oblique elliptica, 

 solidula, epidermide tenui fusca induta; latere antico [i.e. postico) 

 brevi; margine dorsali longe inclinato, ventralibus crenulatis. 2 

 lin. Hab. ? (Mus. Belcher.)" — Unknown to me, but said to be 

 closely allied to pisum, and still more oblique. 



16. N. CRENULATA, A. Adai/is, f. 134, 135. — T. K exigna 

 assimihs, sed major, cute olivacea, sulcis propinquioribus, striis 

 radiantibus subobsoletis, margine ventrali minus arcuato. — Var. ? 

 Pai/tensis. Sculptura nonnunquam ad umbones obsoleta ; lirse 

 radiantes, conspicuse; lunula inferne paululum eminentior, aliquan- 

 tumque angulariter planulata. — Kesembhng exigua, but larger, 

 rather more tapering at the front extremity, and more rounded off 

 at the posterior ventral corner ; the epidermis olivaceous ; the 

 grooves much closer, the radiating sculpture almost obsolete ; the 

 ventral margin less arcuated. — The type (a single individual) looks 

 like a large emgua, but is more compressed in proportion, and the 

 sulci are much closer on its nuclear portion than upon that shell. 

 The lunular area is neither impressed nor groove-defined. — Far.? 

 N. Payfensis, Adams, Proc. Zool. Soc. 1856, p. 51. Sculpture 

 sometimes obsolete on the umboes, the radiating lyrse very dis- 

 tinct ; lunular area rather more angularly depressed, and slightly 

 more projecting below (f. 160, 161). 



17. N. EXIGUA, Soirerby, f. 136. — T. minuta, oblique ovata, 

 longitudine latitudinem multum superante, vahda, ventricosa, niti- 

 diuscula, pallide lutescens, sulcis remotis inclinatis striisque radian- 

 tibus decussatis undique concentrice sculpta. Extremitas antica 

 rotundata, margo ejus dorsalis convexus. Latus posticum brevis- 

 simum, inferne obsolete subangulatum, hand autem prominens. 

 Margo ventralis crenatus, arcuatus, postice acclivis. Regiones dor- 

 sales costeUis, anticis remotis, posticis approximatis, transversim or- 

 natffi. Nates lunulaque liaud eminentes. — Minute, obliquely ovate, 

 decidedly longer than broad, ventricose, of a rather glossy yellowish- 

 white : disks marked throughout with regular coarse concentric 

 grooves, which are distant, shelving, and radiatingly decussated by 

 liner striae : dorsal regions barred across ; the front costellse dis- 



