IKKDALE : NOTES ON POLYl'LACOPHOKA. 127 



When Pilsbry quoted tliis extract lie \M'ote Leptochitona, wliich is 

 quite a different name. Tliere can be no other conclusion than that 

 the name Accuithochitona is correctly introduced as a sub-generic 

 name for the species grouped with Chiton fascmdar is. Though never 

 hitherto used, it claims every right to usage, and fortunately little 

 confusion will be caused by giving the name its due. The name 

 commonly in use is Acanthochites, which date from Kisso, 1826. 

 llisso introduced it from Leach's MS., and it is probable that Gray 

 was also influenced by Leach's proposition. It might be noted that 

 Risso's spelling has been amended to Acanthochcetes, Acanthochitus, 

 and even Acmdhochiton, whilst the species are commonly called 

 Acanthochitons as a vernacular term. 



Though not recorded in Scudder's Nomenclator, Gray's genus-name 

 appears in the synonymy of Accmthochites, Risso, in H. & A. Adams' 

 Genera Recent Xollusca, vol. i, p. 482. 



The genus-name Lepidochitona. 



The consideration of this name naturally follows the preceding 

 discussion. However, here rather radical alterations are necessary. 

 The only species mentioned in conjunction with the name is Chiton 

 marginatus, and this consequently becomes the type by monotypy. 

 Pilsbry (Man. Conch., vol. xiv, p. 67, 1892) included this species in 

 the genus Ischnochiton, placing it in the sub-genus Trachydermon^ 

 Carpenter, 1863, citing as a synonym Craspedochilus, G. 0. Sars, 

 1878. The succeeding year, however, Pilsbry (Man. Conch., vol. xv, 

 p. 63, 1893) admitted that Trachydermon was generically distinct 

 from Ischnochiton, and named as type T.jieclens, Carpenter. Craspedo- 

 chilus, G. 0. Sars, was proposed for C. marginatus alone, and in the 

 List of British Marine MoUusca, prepared by a Committee of the 

 Conchological Society (Jourii. Conch., vol. x, p. 10, 1901), Craspedo- 

 chilus, probably at Sykes' suggestion, was given generic rank, as 

 independent of Tracliydermon. Lepidochitona will theiefore displace 

 Craspedochilus, being exactly equivalent to it. 



Thiele (Revision, p. 116, 1909) makes Trachydermon a genus 

 of his family Callochitouidte, ranking Craspedochilus as subordinate, 

 with sectional rank ; his family Callochitonidse is divided into two 

 sub-families, Trachydermonina? and Callochitoninse. The acceptance 

 of Thiele's classification and the recognition of Lepidochitona would 

 necessitate the following alterations: — 



Family LEPinocHixoNiDiE. 



vice Callochitonid.e. 

 Sub-family LEPiDOCHixoxiNiE. 



vice Trachtdermonin^. 

 Genus Lepidochitona, Gray, 1821 (= Craspedochilus, G. 0. Sars, 

 1878). 



vice Trachydermon, Cpr., 1863. 

 Sub-genus 'Trachydermon, Cpr., 1863. 



In the Proc. Zool. Soc. Lond., 1847, p. 127, Gray introduced the 

 new genus Leptochiton with three species, cinereus, hanleyi, and 



