276 NORRISIA. 



The position of this genus is a little uncertain. Troschel places 

 it in the vicinity of Gibbula, and this is probably its natural posi- 

 tion. Fischer includes it as a subgenus under Gibbula. The 

 peculiar operculum and dentition suffice to give the group generic 

 rank however, in my opinion. The dentition is figured by Dall 

 (Am. Journ. Conch. 1871, pi. 13, f. 6). Young shells are strongly 

 bicarinate, and have an umbilical rib like Monilea. The dentition 

 is figured on pi. 50, fig. 9. 



N. NORRISI Sowerby. PL 61, fig. 30. 



Shell wide, depressed-turbinate ; solid, nearly lusterless, smooth, 

 save for light growth-lines and ill-defined spiral lines ; reddish fawn- 

 colored, black around the umbilicus ; umbilicus large, contracted at 

 its opening ; greenish inside ; spire low-conoidal ; apex minute, sub- 

 acute, spirally striate ; when perfect, the apical whorls are variegated ; 

 sutures plain ; whorls about 6, rapidly widening, nearly plane and 

 sloping above ; the last very large ; aperture rounded-quadrangular, 

 angular above, brilliantly nacreous inside ; peristome thin, simple, 

 columellar margin thickened at the base, and with a very obtuse 

 tubercle there. Alt. 4fc diam. 52 mill., or less. 



1 



me 



Operculum circular! multispiral, nucleus central ; edges of the 

 whorls projecting outsiie, papery and rolled up like a spiral cord. 



Cerros Id., L. Cal. north to . 



Trochiscus norrisi SOWB., Ann. & Mag. N. H. 1838, p. 96. 

 GRAY, Zool. Beechey's Voy., t. 34, f. 14. CHENU, Man. de Conchyl., 

 i, p. 362, f. 2692. CARPENTER, Rep. Brit. Asso. Adv. Sci. 1863, p. 

 665. BALL, Amer. Journ. Conch., vii, t. 13, f. 6 (Dentition^. 

 TROSCHEL, Das Gebiss der Schn., ii, p. 243, t. 24, f. 15. KEEP, 

 West Coast Shells, p. 86, f. 82. Turbo norrisi DESH. in Lam. An. s. 

 vert, ed. 2, ix, p. 221. PHILIPPI, Conchyl. Cab., p. 50, t. 12, f. 5. 

 REEVE, Conch. Icon., f. 54. Trochus norrisi FISCHER, Coq. Viv. 

 (Turbo), p. 45, t. 10, f. 1. Turbo rotellceformis JAY, Cat., 3d ed., 

 1859, p. 3, 1. 1, f. 2, 3. Trochiscus convexus CARPENTER, Ann. and 

 Mag. K H. xv, 1865, p. 180. 



A form very distinct from all others. It is an abundant species 

 about San Diego, Cal. I do not know how far northward it ranges. 

 The dimensions given above are for the largest specimen I have seen. 

 Fischer quotes it from Oregon. 



