FAMILY PATELLIDZ — PATELLOIDA. 163 
Mr. Couthouy, to whom we are indebted for our first anatomical acquaintance with this 
animal, observes, that “‘ perhaps it would be more correct to consider it as a constant variety 
(of P. testudinalis), than as a distinct species ;” and ‘many species have been received as 
valid, upon far narrower distinctions than exist between this and Mr. Say’s shell.” It occurs 
almost universally upon the Eel-grass (Zostera marina), while the testudinalis is attached to 
rocks. 
FAMILY CHITONID. 
ANIMAL without tentacles or eyes, but furnished with a small veil. The branchial apparatus 
formed by a cordon of small pyramidal leaves, around the mantle. Sue. multivalve, 
shield-shaped. 
GENUS CHITON. Linnaeus. Lamarck. 
Animal elongate, obtuse at both ends, and without a very distinct head. Tentacles replaced 
by a small membranous veil, which extends over the mouth; the latter inferior, without 
jaws, and with a small prickly tongue. Fcot elongated, the mantle extending beyond it 
more or less completely ; the gills under the edge of the mantle, particularly behind. Vent 
at the posterior extremity. Generative organs double; one on each side, between the 
leaves of the gills. Shell oval, composed of eight arched pieces arranged in a series more 
or less overlapping each other, their sides imbedded in the skin. 
CHITON ALBUS. 
PLATE X. FIG. 200. 
Chiton albus, Montacu, Test. Brit. 4, 
C. sagrinatus. CoutTHovuy, Bost. Journ. Nat. History, Vel. 2, p. 82. 
C. albus. Gouxp, Invertebrata of Massachusetts, p. 150, fig. 21. 
Description. Shell small: valves with a small beak, minutely crenulate on their anterior 
margin, subcarinate with minute strie ; the surface, under the lens, exhibiting the appearance 
of shagreen. An obsolete diagonal ridge sometimes divides each side into triangular areas, 
but for the most part without any distinct boundary. Margin membranous, covered with 
beaded granules. 
Color. Epidermis a blackish powder, underneath which greyish white; the marginal 
membrane ash-colored, with a narrow black line in the middle surrounding it. 
Length, 0°4. Width, 0°15. 
This species was originally discovered by Mr. Couthouy in the stomachs of fishes off the 
coast of Massachusetts, and described by him under the appropriate name of sagriznatus. It 
has since been referred to the albus of Montagu, and aselloides of Lowe, by Dr. Gould. 
21* 
