HELCIONISCUS. 123 



lusterless, sculptured with fine and rather close radiating riblets, 

 sometimes subobsolete. Brownish or tawny, the riblets often 

 lighter, usually mottled with whitish toward the apex. 



Interior bright silvery, the central area of a deep red-bronze, 

 muscle-scar snowy-white, surrounded with red-bronze, 



Length 61, breadth 58, alt. 14 mill. 



Coast of Chili at Valparaiso and Saint Vincent. 



P. clypeater LESSON, Voy. de la Coquille, Zool., p. 419, (1830). 

 REEVE, Conch. Icon., f. 38", 38b. 



A nearly circular, depressed shell, having the bronze-brown color- 

 ing characteristic of Patinella. The interior sometimes has no white 

 horse-shoe ; and in some examples the silvery outer zone is consider- 

 ably invaded by bronze stains. 



This species has been reported from California, Lower California 

 and Japan, but not correctly. 



Genus HELCIONISCUS Ball, 1871. 



Helcioniseus DALL, Amer. Journ. Conch, vi, p. 227, (type Patella 

 variegata Reeve). THIELE, in contin. Troschel's Das Gebiss der 

 Schnecken, ii, pt. 7, 333 (full discussion and figures of the dentition). 

 Cellana H. ADAMS, P. Z. S. 1869, p. 274, (type N. cernica.) 



The gill-cordon is interrupted in front. 



There are no epipodial processes or ridge on the sides of the foot. 



The formula of teeth is 3 ( 1 111 1 ) S . 



The radula is long and spirally rolled. The rhachidian tooth is 

 narrow, with a variously shaped forward appendage. The inner 

 lateral has an outward wing, and a simple, long, cusp ; the outer 

 lateral has an inner long point with an outer side-cusp, besides a 

 short, mostly rounded longitudinal cutting-edge. The marginal 

 teeth are characteristic in appearance, the posterior part being 

 divided from the anterior, the connection being so thin as to be im- 

 perceptible. The inner marginal tooth has a cusp on its front end 

 (pi. 74, fig. 6, P. capensis Gmel.) 



The shell is conical, apex subcentral or subanterior ; inside hav- 

 ing a silvery and mica-like luster. 



Distribution, Indian and Pacific Oceans, but not found on the 

 American shores north of Chili. No species have been found in 

 the Atlantic Ocean. 



This group is closely allied to the Patinella section of Nacella, 

 having a very similar radula. It differs in the lack of an epipodial 

 ridge, in having the gill-cordon interrupted, and in the silvery- 



