328 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



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

 spicules, as in T. marmorea. 



? Tonicella Sitkensis. 



Chiton Siikotsis Midd. Bull. Acad. Sci. St. PtStersb.vi, p. 121, 1846; Mal.Eoss. 



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

 Totiicia Sitkensis H. & A. Adams, Geu. Rcc. Moll, i, p. 474, 1854. 

 Not Chiton Sitlccn&is Reeve, Couch. Icou. sj). 55, 1847. 



?T. t. externa cTepressa; tegmentum loB^ausculum, areis lateralibus 

 iudistinctis, sub leiite sj^arsim granulosum, rubicundum; limbi lievius- 

 culi epidermis zonalis submicroscopio stroma exhibet spinulis latenti- 

 bus erectis munitum; v. ant. 8-, v. post. 10-, v. centr. 1-fissata; brancliioe 

 postica?,, parcfe, no. circ. 24. Lon. 10, Lat. 6 mm. Div. 130°. 



Sab. — 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 nuich 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. mhmarmoreus^ and may well be a 

 j'oung specimen of one of its numerous varieties. 



Genus SCHIZOPLAX DaU. 



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



Tonicia sp. H. & A. Adams. 



Schizoplax Cpr. MS. (subgenus of Tonicella). 



Testa et zona Tonicellse simulans ; valvfe centrales sulco jugali medi- 

 ano, antico argute incisoe ; branchice 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 specunens obtained 

 by us api^ear to be the first obtained by any one since the original spe- 

 cimens of Middendorf. 



Schizoplax Brandtii. 



Chiton Brandtii Midd. Bull. Acad. Sci. St. P^tersb. 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. 

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



S. t. ovali, lougiori, aug-ustiori, satis elevata; jugo rotundato; oliva- 

 ceo-fusca, caeruleo sen strigata, sen maculata sen nebulosa; sfepeirregu- 

 laiiter castaneo; mucrone centr. irregulariter subplanato; v. post, om- 

 iiiuo satis regulariter excurvata; ar. jug. noimisi colore definitis, ar. lat. 

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



