2 LEPIDOPLEURUS. 



spongy. Girdle downy, having small, tufted pores. Type, H. set- 

 ulosum Cpr. 



A A. Valves partly covered, the exposed portions small and sepa- 

 rated. 



Genus IV. MtCROPLAX Adams & Angas, 1804. 



Insertion plates smootfi and thin, well developed in all the valves. 

 Sutural plates and sinus obsolete. Girdle thin, most minutely gran- 

 ular, not poriferous. Type, M. grayi Ad. & Ang. 



Genus I. LEPIDOPLEURUS Risso, 1826. 



Lepidopleurus Risso, Hist. Nat. 1'Eur. Merid., iv, p. 267, 1826, 

 (in part ; first species L. cajetanus Poli). SARS., Moll. Reg. Arct. 

 Norv., 1878, p. 110. Not Lepidopleurus of H. & A. Adams, Car- 

 penter, Dall, et al. Leptochiton GRAY, Proc. Zool. Soc. Lond. 1847 y 

 p. 127 ; Guide Moll.B.M., p. 182, 1857. CARPENTER, MS. p. I 

 DALL, Proc. U. S. Nat. Mus. 18*78, p. 314. Leptochiton, in part, of 

 H. & A. ADAMS, Gen. Rec. Moll, i, p. 473, and of CHENU, 

 Manuel, i, p. 381. 



In Lepidopleurus the insertion plates are completely absent; the 

 girdle is narrow, with minute striated or smooth scales, and some 

 longer scales at the edge. 



The present genus has hitherto been known as Leptochiton, but 

 the rejection of that name seems to be inevitable as will be seen 

 from the following : 



History of the name Lepidopleurus. The first publication of 

 Lepidopleurus was in Risso's Histoire Naturelle des principales pro- 

 ductions de PEurope Meridionale, vol. iv, p. 267, 1826, where it is 

 quoted as of Leach's ms. It is characterized as having the triangular 

 lateral areas elevated and the girdle covered with small scales, and 

 in it are included (711) L. cayetanus Poli, (712) L. corallinus n. sp. 

 and (713) L. sulcatus n. sp. Of these, the first species belongs to 

 the group which Gray subsequently named Leptochiton, and the 

 two latter belong to the genus Chiton as restricted to Linnaeus' 

 type. It is therefore evident that if used at all, the name Lepido- 

 pleurus can properly be used for Leptochiton only. It is greatly to 

 be regretted that it was not so used by Gray, as much subsequent 

 confusion would have been avoided. The republication of the 



