26 NUCUMD.B. 



responding modification of slopes and ventral arcuation) varies 

 mucli in different individuals : the posterior smoothness seems a 

 constant character. 



43. L. MiCANS, A. Adams, f. 100. — T. ovali-acuta, postice re- 

 pente rostrata, fequihiteralis, subventricosa, ante plicara umbonalem 

 obsoletam superne retusa, cute nitida cinerea induta, undique con- 

 centrice sulcata. Extremitas rostri recurvata, angularis, subcen- 

 tralis. Margo dorsalis antice satis dcclivis ; postice rectiusculus, 

 demuni incurvatus; ventralis valde arcuatus, utrinque, postice 

 prjBsertira, raultum acclivis. Area magna, ovali-lanceolata, longi- 

 tudinaliter crasse rugosa. Lunula acute definita, satis magna, 

 transversira porcata. — Peaked-oval, convex or subventricose, 

 scarcely gaping, with a ulossy, somewhat iridescent, cinereous 

 epidermis, graven throughout (dorsal areas excepted) with con- 

 centric sulci, which are shelving in front, and whose intervals be- 

 come costse at the umboes and posteriorly : umbonal ridge region 

 not elevated. Sides equal or very nearly so : front extremity 

 attenuatedly rounded ; hinder end abruptly beaked, the tip re- 

 curved, angular, subcentral. Front dorsal slope moderate, plano- 

 convex : hinder dorsal slope decided, straightish, incurved at the 

 end. Ventral margin much arcuated, much rising at both ends, 

 especially behind. Escutcheon large, oval-lanceolate, coarsely 

 wrinkled lengthways, defined by the projection of the umbonal 

 ridge, pouting. Lunule shar[)ly defined, rather large, barred 

 across with short ridges. — The posterior ridge is preceded near 

 the beaks by a marked refusion, and there is an obsolete narrow 

 indented ray in front of the valves. 



44. L. CoNHADi, Eanleij, f. 101. — T. subovato-acuta, postice 

 longior et acutissinie acuminata, valde inarquilateralis, radii im- 

 pressi expers, cute subolivaceo-tlava induta, costis crassis concen- 

 tricis (ad margineui plica; nnibonalis angularem plnribns), et sulcis 

 superne latis, infernii angustis, undique sculpta. Margo dorsalis 

 antice subdeclivis; postice rectiusculus, declivis. Area magna, 

 angulatim definita, inferne plicato-corrugata. Lunula nulla. — 

 Peaked-subovate, very inequilateral, subventricose (very gradually 

 diminishing in convexity behind), devoid of any trace of an in- 

 dented ray, clothed with a scarcely lustrous subolivaceous-yellow 

 epidermis, concentrically ribbed throughout. Ribs coarse, with 

 smooth intervals that above are as broad as the ribs, below are 

 mere sulci, peculiarly crowded by the addition of interstitial ones 

 on the angular margin of the posterior ridge. Anterior side short, 

 tapering and rounded at the extremity : posterior side gradually. 



