ISCHNOCHITON. 125 



genuine Ischnochitons in the Gulf fauna is remarkable, especially as 

 so many species are found further north. (Cpr. MS.) 



Section Lepidozona Pilsbry, 1892. 



Lepidopleurus CARPENTER (Table of Regular Chitons, 1873) ; 

 DALL, Proc. U. S. Nat. Mus. 1878, p. 331, type L. mertensii Midd. 

 Not Lepidopleurus of Risso, Hist. Nat. Eur. Merid. iv, p. 267, 

 1826, nor of H. & A. ADAMS, 1858, nor of CARPENTER, Mazat. 

 Cat. 1857. 



Valves having sharp but somewhat rugose and thick insertion 

 teeth, and (typically) the sinus is delicately toothed within. Girdle 

 covered with convex scales, usually smoothish. Type I. mertensii. 



This section differs from Ischnochiton not only in having the gir- 

 dle scales convex and smooth or but slightly striated, but also in 

 the toothed sinus. It is, however, an artificial group, the species 

 being more closely related to a number of diverse Ischnochitons than 

 to each other. Numerous transitions from the smooth convex 

 scales to flat striated scales occur, the variation in degree of stria- 

 tion being considerable in some species. This section in its present 

 limits is therefore merely a temporary expedient for convenience in 

 identifying species. It should rank as a section under Ischnochiton 

 s. ., rather than under Ischnoradsia, to which group these species 

 have no especial affinity. The status of the name Lepidopleurus 

 has been discussed on page 2 of this volume. 



I. MERTENSII Middendorff. PL 26, figs. 20-26. 



Shell oval, elevated, with angular dorsal ridge, and straight side- 

 slopes. Varying in color from orange-red to claret-red, or even 

 dark red-brown, and either unicolored or speckled and blotched 

 with white. 



The lateral areas are elevated, and sculptured with radiating rows 

 of elevated pustules standing upon a smooth, almost flat ground; 

 the pustules of the sutural row often irregular. Central areas hav- 

 ing acute, narrow, parallel raised riblets, the intervals between them 

 regularly latticed across, except at the dorsal ridge, where the 

 riblets have a tendency to diverge, and the cross-hatching is obsolete. 

 End valves radially pustulose. Mucro central, low, flat and incon- 

 spicuous. 



Interior white or blue-white, the median valves when detached 

 showing broad red-brown rays posteriorly, the end valves with cres- 



