LEPTOTHYPvA. 245 



the lower margin fluted; columella arcuate, broad, excavated at 

 position of tlie umbilicus, and terminating in a tooth-like promi- 

 nence below. Alt. 45, diam. 55-62 mill. 



Western America, Acapulco to Vancouver Id. 



Operculum (pi. 60, figs. 68, 68a) inside deep brown, convex at up- 

 per, concave toward lower margin ; outside smooth, or rugose at the 

 distal extremity, and white, brownish toward the nucleus. 



Synonyms, Trochus glbherosus Zealandlce Novcc etc., Chemnitz, 

 Trochus gibberosus (or Pachypoma gibberosum) "Chemnitz" of au- 

 thors, (not Trochus inaequalis umbilieatus etc., Chemnitz,= jr. 

 incequalis Gmel. a species of Trochid(e), T. diadematus Yal., and T. 

 ochraceus Phil. 



The name inequalis Martyn, here adopted for this species, has four 

 years priority over Chemnitz's name. Besides, the latter author 

 was a polynomialist, and merely copies Martyn's excellent figures 

 of the species. 



Genus LEPTOTHYEA (Carpenter^ Dall, 1871. 



Shell small or minute, globose-depressed, solid, compact; umbili- 

 -cate or imperforate, whorls .S-7, spirally sculptured, the last generally 

 somewhat deflexed at the aperture; aperture subcircular, white and' 

 nacreous within; columella generally but not always bluntly den- 

 ticulate near the base. Operculum subcircular, nearly flat or 

 concavo-convex, inside with a very thin corneous layer, slightly 

 convex, w'ith many gradually increasing wd^orls, the nucleus sub- 

 -central; outside calcareous, subspiral, with a slightly convex con- 

 centric elevation or ridge around the margin, most prominent at 

 its termination, the middle portion concave and more or less rugose. 



The species are numerous, inhabiting nearl)^ all tropical and sub- 

 tropical seas; but most numerous in the Pacific. 



The synonymy includes Collonia Gray (in part), Collonia of most 

 authors, Leptonyx and Homalopoma. Carpenter (pi'eoc), Cantrainea 

 Jeftreys, Ca.ntraiiieia Fischer, Anadema H. & A. Adams. The 

 genus is very homogeneous, and neither of the subgenera proposed, 

 (^Cantrainea Jeff", for L. carinata, and Anadema Ads. for L. coelata 

 Ad. have sufficient characters for any systematic rank. 



The characters of the dentition are discussed on p. 188. The 

 rank and position of this group has been the subject of considerable 

 controversy; but partly, perhaps, on account of the minute size of 

 the species, partly because of the scattered and inexact condition of 



