198 MAZATLAN UNIVALVES 
Genus CHITON, Linn. 
Cliton, pars, auct.—H. & A. Ad. Gen. vol: i. p.474.—Acan- 
thopleura, Guild.; Gray in Proc. Zool. Soc. 1847, p. 67.— 
Margin spinose: insertion-plates in terminal valve many- 
lobed, in middle valves bi-lobed. 
257. CHITON FLAVESCENS, 7. s. 
Ch. t. ovatd, valde depressa (ad angulam 150°) flavidd, 
aurantio maculata ; valvis latis, marginibus subrotundatis, 
tnterstitiis curvatis, valde mucronatis ; areis lateralibus et jugo 
indistinctioribus ; mucrone parvo, superiore ; totd superficie 
granulis rugulosis confertiin instructa, haud punctulaté ; limbo 
pall crasso, sublevi, ad marginem spinulis tenuibus, erectis, 
planatis instructéd ; valvarum lobis, magnis, arcuatis, sinu 
maximo; marginibus valvuarum intermediarum jissura duas in 
lobas divisis, quarum una parva, lineis punctorum utrdque in 
parte ad jugum decurrentibus ; valvarum ultimarum marginibus 
subacutis, fissuris circiter x. 
This is the least uncommon of the small Chitons, six speci- 
mens having been found of it. It is distinguished by its yellow 
colour, great depression, and small strong mantle margin, 
without covering, except at the margin where a fine row of 
transparent flattened hairs may be seen. The smaller lobe on 
the margins of the inner valves is bounded by two rows of 
holes which proceed to the jugum. Long. ‘16, dat. *11, alt. °3. 
Another specimen, rolled into a ball, is larger. 
Hab.—Mazatlan ; on shells, very rare; L’pool Col. 
Tablet 906 contains the largest specimen; another in situ 
on a broken crevice of Crepidula; and 2 separate valves. 
Genus ACANTHOCHITES, Risso. 
Gray, Proc. Zool. Soc. 1847, p. 66: H. & A. Ad. Gen. vol 1. 
p. 482.—Chiton, pars, avct. Mantle with tufts of bristles. 
958. ACANTHOCHITES ARRAGONITES, 2. S. 
A. t. elongata, elevaté (ad angulam 110°), pallido-fusca, 
olivaceo et roseo varie picta : valvis intermediis valde mucronatis, 
interstitiis a mucronibus valde divergentibus ; jugo lato, pallido, 
