206 MAZATLAN UNIVALVES 
= Patella opea, teste Rve.: non Nutt., in Rve. Conch. Ic. 
sp. 79, pl. 29, f. 79, a, 6. (Sandwich Isl.) 
Var.=P. discors, jun. P. P. C. Cat. prim. 
The following W. Indian species in the Br. Mus. are closely 
analogous: Lottia lineata, Tranquebarica, and pulcherrima, 
(Guilding.) 
The exquisite beauty of this “most lovely species” (as 
Menke deservedly calls it), both for the shading of the colours 
and the delicacy of the penciling, cannot be described. The 
prevailing tints are a reddish brown outside, more or less 
mottled or striped with white ; inside a prevailing white, more 
or less penciled or fretted with brown, and a border, sometimes 
white with a tessellated penciling of brown; sometimes a 
delicate fawn shading into a pinkish or slightly greenish tinge, 
with or without penciling. The body mark is of a dark lus- 
trous brown, or very light witha greenish tinge, or nearly 
absent. It is large for the size of the shell, more or less 
removed from the margin. The young shells of A. mutabilis, 
Mike. ave a variety of this species; which I unfortunately 
distributed at first as the young of P. discors, with which it 
has really no connection. The colourless and worn shells of 
A. mesoleuca and A. fascicularis are very like each other; but 
as their general habits are very distinct, it is necessary to keep 
them apart. In shape, A. fascicularis is much longer, and 
generally considerably smaller. The standard colour of A. 
mesoleuca is green, of A. fascicularis red. In A. mesoleuca 
the markings are laid on with stripes and patches, in A. fasci- 
cularis with very fine pencilings. In the latter, the outline of 
the body mark is much more regularly gathered up into points 
with concave margins between, the points often making regular 
lines radiating from the centre. The surface of A. mesoleuca 
is covered with granulose ribs with smooth interstices and a 
very thin smooth epidermis; that of A. fascicularis is very 
much more finely marked, shewing under the glass smooth 
ribs with the interstices extremely finely cancellated with 
very close slightly rugose concentric striz, covered with an 
extremely thin rather velvety epidermis. The surface of A. 
fascicularis is much more generally abraded ; and as the young 
shells were not uncommon in the Spondylus and Chama 
washings, while not one was found of A. mesoleuca, it is pre- 
sumed that their station is different. The apex is sometimes 
brown, sometimes white; and in the smallest specimen, *035 
by ‘025, shews no trace of being spirally recurved. The young 
