332 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



spongiosis; sinu ininore, laminato, lamina atroque latere et interduin 

 in medio fissataj zona squamulis perparvis, solidioribus, irregulariter 

 instructis ladvibus, instructs ; branchiis fere ambientibus, per valvas 

 VI posticus continuis. Lon. 40, Lat. 26 mm. Div. 135°. 



Hab. — Sitka, Port Etches, 9-18 fins., gravel, rare; south to Puget 

 Sound. Six specimens examined. 



This rare and fine species is not particularly handsome, being of dull 

 and livid colors, but is peculiarly characterized by the straight trans- 

 verse ribs on the dorsal areas, with spongy interspaces, and by the 

 pretty regular division of the lateral areas into three well-marked radi- 

 ating costse, which are separated in the insertion-plate by two fissures. 

 Xo other species of the region resembles this in sculpture. Muzzle with 

 a pectinated margin in front produced into rounded lappets at the 

 corners. Gill-rows as long as the foot, containing each 28-35 branchiae. 

 Veil absent. Mantle-edge plain, narrow. There is a small spherical 

 lump on each side of the girdle just behind the posterior ends of the 

 gill-rows, which are turned out toward the girdle and widely separated 

 behind. The anus is large, median, and crenate, opening on the upper 

 part of the hinder end of the foot. No ovarian openings could be 

 detected, and the species presents some peculiarities which call for 

 further research with more material. 



Subgenus Lepidopleurus s. s. Cpr. 



Lepidopleurus Mertensii. 



Chiton Mertensii Midd. Bull. Ac. Sci. St. Pe'tersb. vi, p. 118, 1846. 



Chiton (Phcenochiton, Hamachiton, Stenosemus) Mertensii Midd. Mai. Ross. p. 34, 



125, pi.' xiv, f. 1-3 a-h, 1847. 

 Leptochiton Mertensii H. & A. Adams, Gen. Rec. Moll, i, p. 473, 1854. 



L. t. colore rubido, interdum intensiore nebuloso; mucrone subcen- 



trali, haud elevato; intas v. term. 9-12-, centr. 1 fiss.; dent, acutis; sub- 



grundis majoribus; sinu lato, planato, larvi; zona rubida seu pallidiore, 



squamis ovoideis, nitentibus, hevibus vix regtdariter confertissime im- 



bricata. Lon. 20, Lat. 6 mm. Div. 100°. 



Hab. — Sitka and vicinity, south to Monterey, Cal. Many specimens 



examined. 



Middendorf 's description and figures of this shell do not agree well 

 together. Its fine red color, sharp and promiuent sculpture, usually 

 free from erosion or nullipore, and beautifully shining and regular scales, 

 render this one of the most attractive and easily recognized of the 

 Alaskan Chitons, There are no others in that region likely to be con- 

 founded with it. It rarely shows a white valve or a dash of white on 

 some of the valves. 



The soft parts of this species are whitish. The anus is on a papilla. 

 Mantle-edge narrow, granulose, forming on each side behind the last 

 branchia a rounded lump or tumor. Near this the ovarian openings 

 were thought to be detected. Muzzle semicircular, cornered behind on 



