6 AMPHINEURA . [Polyplacopliora, 



SUBORDER 1. EOPLACOPHORA, Pilsbry. 



Tegmentum coextensive with articulamentum, or the latter pro- 

 jecting in smooth unslit plates. 



Fam. LEPIDOPLEURID^-E, Pilsbry. 



Leptoidea, Carpenter. Leptochitonidce. Ball, " Blake " Gastrop., 1889. 414. 

 Genus Holochiton, Fischer, Man.. 877. 



Chitons in which the head and tail valves are similarly articulated, 

 and having the insertion plates either obsolete or, if present, without 

 slits. Girdle finely scaly or bristly ; gills short, posterior. 



This family is readily known by the entire absence of insertion 

 plates, or the simple unslit character of them when present. The living 

 species are few in number, and mainly either northern in distribution 

 or living at considerable depths. All of the Paleozoic Chitons yet 

 known belong to this family, and this fact, together with the weak, 

 imperfect articulation of the valves, causes us to regard the Leptoids 

 as the most primitive of the existing groups. (Pilsbry.) 



Genus 1. LEPIDOPLEURUS, Risso, 1826. 



Lepidopleurus, Risso, Hist. Nat. de 1'Europe Merid., iv, 1826, 267 (in part). 

 First species: L. cajetanus, Poli. Not Lepidopleurus of H. and A. 

 Adams, Carpenter, Dall, &c. Leptochiton, Gray, P.Z.S., 1847, 127. 

 Leptochiton, in part, of H. and A. Adams, G.R.M., i, 473 ; and of Chemi, 

 Man., i. 381. (Pilsbry.) 



Insertion plates absent. Girdle with minute, gravelly, smooth or 

 striated scales, usually with a marginal fringe of longer scales. 



From the Southern Hemisphere very few species are known : two 

 from Tasmania, Australia, and New Zealand, and one each from 

 the Kerguelen Islands, South Georgia, Straits of Magellan, and the 

 Antarctic (Voy. du S.Y. " Belgica "). 



1. Lepidopleurus inquinatus, Reeve, 1847. Plate 2, fig. 1; Plate 3, 

 fig. 1. 



Lepidopleurus inquinatus. Reeve, Conch. Icon., Chiton, pi. 23, f. 154; Man. 

 Conch. (1), xiv, 90. L. liratus, Adams and Angas, P.Z.S., 1864, 192 

 Man. Conch. (1), xv, 101 ; P. Mai. S.. ii, 86. 184. 



Shell oblong-ovate, small, yellowish-brown, longitudinally finely 

 ridged. Anterior valve very finely radiately striate, with a few con- 

 centric grooves. Intermediate valves with the central areas longi- 

 tudinally finely grooved, the sculpture extending over the jugum : 

 lateral areas slightly raised, with concentric fine wrinkles and a few 

 distinct furrows near the margin ; valves broadly rounded. Posterior 

 valve with fine longitudinally arranged ridges on the central area, 

 fine concentric riblets and a few distinct furrows on the posterior 

 area, mucro central, the posterior slope concave. Girdle covered 

 with minute scales, which are rounded, convex, and strongly striated. 

 Colour of the valves light yellow with a brown spot along the summit 



