OP CONCHOLOGY. 33 



broad emarginated cusp nearly twice as long as the base. The 

 laterals grow broader and shorter toward the edge. The outer 

 thirteen laterals are tridentate. The inner laterals from the 

 eleventh to fifteenth are bidentate. The formula is o0-l-30 or 

 15"15*1'15*15. There are about two hundred rows in all. 

 The following species belong to the second section : 



SiPHONARiA THERSITES, Cpr., Annals and Mag. Nat. Hist., 

 1864, xiv, p. 425. 



Cpr. (MSS.) Suppl. Rep. to the Brit. As., 1863, pp. 627 

 and 676. Stearns, shells of Alaska, Pr. Cal. Ac. Sci. 

 Vol. Ill, p. 334. 



Testa parva, tenui, baud elevata, valde inequilateral!, dense 

 nigro-castanea, laevi seu interdum costulis paucis, obtusis, obso- 

 letis, radiatim vix ornata ; epidermide Inevi, tenui, fugaci ; costa 

 pulmonali intus et extus valde conspicua, tumente ; vertice 

 obtuso, plerumque ad quadrantem, interdum ad trientem totius 

 longitudinis sito ; intus intense nigro-fusco, margine acuto. Lon. 

 •46, Lat. -33, Alt. -17 in. 



Hah: Neeah Bay ; Sitka ; Vancouver's Island ; Fort Simpson ; 

 N. W. C. Am. 



The external appearance of the animal is very plain. The 

 mantle edge, sides of the foot, and head are smooth and even. 

 The lobe is stout and short. The head is small, and the eyes 

 could not be found with a high power. The soft parts are en- 

 tirely contained within the shell. The color in spirits was a 

 dusky slate-color. 



The jaw is simple, arcuated and rounded at the ends. The 

 rhachidian tooth is slender with a simple pointed cusp. 



The inner nine laterals are provided with an oblique, equi- 

 bidentate cusp. The tenth, eleventh and twelfth are tridentate. 

 The remainder are much broader and shorter, tridentate ; the 

 central point more prominent than the others, and, in the thir- 

 teenth, fourteenth and fifteenth slightly emarginate at the tip. 

 The cusps grow less conspicuous toward the outer edge, and in 

 the outer three teeth are hardly perceptible. The formula is, 

 22-1-22, or 7-3-3-9-1-9-3-3-7. 



This species having been obtained in lat. 57° N., is probably 

 the most northern representative of the genus. 



SiPHONARiA Tristensis, Sby. 



^S*. Tristensis, Sby., Genera of Shells, fig. 3. Eve. Mon. Si- 



phonaria, PI. V, fig. 23a, b. 

 Patella Tristensis, Leach, teste Rve. 

 Siphonaria Lessoni, Blainv., teste Rve. 



3 



