206 MAZATLAN UNIVALVES 



= Patella opea, teste JRve. : nou Nutt., in Rve. Conch. Ic. 



sp. 79, pi. 29, f. 79, a, b. (Sardwich 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, 



(Gruilding.) 



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 with a 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, 

 M^ke. are 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 strise, 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 



