PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 305 



dian line; tail notched 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 Wossnessenskii 

 by its blackish and proportionately much narrower girdle, and by a sort 

 of prolongation 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- 

 nessenskii 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 dry 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 muscosa and the dark, smooth 

 JEtindsii could be properly combined under one name with each other or 

 with the finely reticulated and painted lignosa. But the study of a large 

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

 anywhere in a fully representative series, beginning with coarsest oiliaia 

 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 sculpture with 

 a downy than with a bristly girdle. However, even this occurs. On 

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

 which, if only the characters were constant, every one would acknowledge 

 as good species. 



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

 penter, had both species under his observation, and did not observe it. 

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

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

 named in 1S32, and the former was renamed Colliei, by Reeve, in the 

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

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

 Carpenter became convinced that the undescribed M. Simpsoni Cray was 

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

 Chiton Esclisclwltzii was merely a young ciliata. Dr. Gould's original 

 types have been consulted during the preparation of this description. 



Mopalia Wossnessenskii. 



Chiton Wossnesscnslii Midd. Bull. Imp. Acad. Sci. St. TVtcrsb. t. vi, p. 119, 

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



Chiton (Hamachiton, riatysemus) IVossncssenskii Midd. Mai. Bees. 1. 0. p. 3-1, 

 1847. 



Chiton coelatusTlcexQ, Conch. Icon. Mon. Chiton, pi. xvn, f. 101, 1*47 (100. err.).— 



H. & A. Adams, Gen. Ree. Moll, i, p. 475, IBM. 

 Mopalia Kcnnerleyi Carpenter, Suppl. Rep. Br. Assoc. 1863, p. Gl*; Pioc. Phil. 



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

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

 M. Kcnnerleyi var. Swanii Cpr. Suppl. Ren. 1. C. p. 64*, 1863. 



M. t, valvis haud antice apicatis; v. post, extus valde sinnatfi; intus 



v. post, late ad caudam sinuata, et v. centr. 1 , v. ant. 8- (rariua '•>-, 10 i 



Proc. Nat, Mus. 78 20 Feb. 14, 1 #79. 



