328 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



and furnished at its extreme margin with a fringe of fine spiny hairs or 

 spicules, as in T. marmorca. 



? Tonicella Sitkensis. 



Chiton Sitkensis Midd. Bull. Acad. Sci. St. Pdtcrsb.vi, p. 121, 1846; Mai. Ross. 



i, p. 112, t. xiii, f. 1-2, 1847. 

 Tonicia Sitkensis H. & A. Adams, Geu. Rec. Moll, i, p. 474, 1854. 

 Not Chiton Sitkensis Reeve, Conch. Icon. sp. 55, 1847. 



?T. t. externa depressa; tegmentum laeviusculuni, areis lateralibus 

 indistinetis, sub lente sparsim granulosum, rubicunduni; limbi lawius- 

 euli epidermis zonalis submicroscopio stroma exhibet spinulis latenti- 

 bus erectis munition; v. ant. 8-, v. post. 10-, v. centr. 1-fissata; branchiae 

 postiese, parcse, no. circ. 24. Lon. 10, Lat. 6 mm. Div. 130°. 



Hab. — Sitka, one specimen (Midd.). 



The above species described by Middendorf, if not a variety of one of 

 the others, has not yet been identified or collected by any other natural- 

 ist. His description differs very much from his figures, while the ante- 

 rior teeth are figured as grooved outside,* if correct, an unusual charac- 

 ter. It is said to be nearest to T. submarmoreus, and may well be a 

 young specimen of one of its numerous varieties. 



Genus SCHIZOPLAX Dall. 



Schizoplax Dall, Proc. Nat. Mus. p. 2, Jan. 1878. 



Tonicia sp. H. & A. Adams. 



Schizoplax Opr. MS. (subgenus of Tonicella). 



Testa et zona Tonicella} simulans; valvse centrales sulco jugali medi- 

 an*), antico argute incisse; branchiae subambientes. 



For this remarkable form, which is distinguished from all other known 

 Chitons by the median slit in all the central valves, I propose to adopt 

 the MS. name suggested by Dr. Carpenter on Middendorf 's figures, rais- 

 ing its value, however, to the rank of a genus. The specimens obtained 

 by us appear to be the first obtained by any one since the original spe- 

 cimens of Middendorf. 



Schizoplax Brandtii. 



Chiton Brandtii Midd. Bull. Acad. Sci. St. P6tersb. vi, p. 117, 184G; Mai. Ross, 

 i, p. 128, 1847. 



Chiton (Hamachiton, Stenosemus) Brandtii Midd. Sib. Reise, p. 174, t. xv, f. 

 1-6, 1851. 



Tonicia Brandtii H. & A. Adams, Gen. Rec. Moll, i, p. 474, 1854. 



Schizojrfax Brandtii Dall, Proc. Nat. Mus. p. 2, Jan. 1878. 



S. t. ovali, longiori, angustiori, satis elevata; jugo rotundato; oliva- 

 ceo-fusca, caeruleo seu strigata, seu maculata sen nebulosa; s.nepe irregu- 

 la liter castaneo; mucrone centr. irregulariter subplanato; v. post, onv 

 nino satis rcgulariter excurvata; ar. jug. nonnisi colore definitis, ar. lat. 

 vix definitis, tota superficie keviore, sub lente conspicue quinc. granu- 



