(liaii line; tail uotclied in the young, but not in the adult; tail-sinus visi- 

 ble outside; girdle with few and short hairs. 



This species can be distinguished from all varieties of Wossnessensldi 

 by its blackish and proportionately much narrower girdle, and by a soi't 

 of ])rolongation of the external layer of the shell forward under the apex 

 of the next anterior valve in the median line, forming a sort of anterior 

 false apex, which is hidden until the valves are separated. In Woss- 

 ncssensldi this part is squared off, the girdle is yellowish (when alive), 

 and the valves are much less transverse. 



It will be surprising if those who have only observed these animals by 

 a, few diy specimens in collections are willing to accept the synonymy 

 above given. I confess that not long since I would have been unwilling 

 to believe that the rough, bristly, typical mnscosa and the dark, smooth 

 llindsii could be jiroperly combined under one name with each other or 

 Avith the iinely reticulated and painted lignosa. But the study of a largo 

 nudtitude of specimens has convinced me no arbitrary line can be drawn 

 anywhere in a fully representative series, beginning with coarsest ciliata 

 and ending with a practically smooth Hindsii. The characters of girdle, 

 .sculpture, and form are not only variable in themselves, but are found 

 variably combined, except that it is rarer to find coarsest sculx>ture with 

 a downy than with a bristl}' girdle. However, even this occurs. On 

 the other hand, out of such a series a dozen forms might be selected 

 A\'hich, if only the characters were constant, every one would acknowledge 

 as good species. 



In his description of Wossnessenslcii, Middendorf, according to Dr. Car- 

 j)enter, had both sj^ecies under his observation, and did not observe it. 

 His figures, however, belong solely to the following species. Sowerby's 

 srtosus, in the Zoology of the Blossom's Voyage, is not his species so 

 named in 1832, and the former was renamed CoUiei, by Eeeve, in the 

 Conch. Iconica. The seidptnre figured by Sowerby was not character- 

 istic; Eeeve's figure is better. From an examination of the type, Dr. 

 Carpenter became convinced that the undescribed M. Simpsoni Gray was 

 identical with lignosa. There is very little doubt that Middendorf*s 

 Chiton Uschscholtzii Avas merely a young ciliata. Dr. Gould's original 

 types have been consulted during the preparation of this description. 



Mopalia 'Wossnessenskii. 



Chiton Tfossnesscnslii Midd. Bull. Imp. Acad. Sci. St. Potersl). t. vi, p. 119, 



1847 (pars); Mai. Rohs. i, p. 101 (diagn. maj. pars), pi. xi, f. 1-2, 1847. 

 Chiton {Hamachiton, riati/semiis) Wossnessenskii Midd. Mai. Ross. 1. c. j). 34, 



1847. 

 Chiton codatus Reeve, Couch. Icon. Mou. Cbitou, i^l. xvii, f. 101, 1847 (loc. err. ).— 



H. & A. Adams, Gen. Rec. Moll. 1, p. 475, 1854. 

 Mopalia Kennerlei/i Carpenter, Sujipl. Rex>. Br. Assoc. 18GI5, p. ()4H; I»roc. Phil. 



Acad. Nat. Sci. April, 1865, p. 59. 

 Mopalia Grayi Carpenter, Suppl. Rep. 1. c. p. 603, name only. 

 M. Kennerleyi var. Swanii Cpr. Su^ipl. Rep. 1. c. p. 648, 1833. 



M. t. valvis hand antice apicatis; v. post, extus valde sinuata; intus 



v. post, late ad caudam sinuata, et v. centr. 1-, v. ant. S- (rarius 9-, 10-) 



Proc. Nat. Mus. 78 20 Fet). 14, 1879. 



