OF CONCHOLOGY. 277 



Not Helcion, Stoliczka, Pal. Indica, ii, p. 323 ; Pictet, Mat. 

 Pal. Suisse, 3rae ser. p. 717 ; nor D'Orb., Voy. Am. Mer. 

 V, p. 703 ; nor Jeffreys, Brit. Conch, iii, p. 242. 



" Shell ovate, radiately ribbed (pectinated) ; apex submargi- 



nal, anterior ; aperture ovate ; edge crenated. Gill interrupted 



over the head, of small and filiform strands." Gray, Guide, p. 

 176. 



Type Helcion pectinatus, Lin. 



Gmelin, Syst. Nat. i, part vi, p. 3710, No. 93. 



Habitat. Mediterranean. 



The shell of this unique and typical species is distinguished 

 by its pectinated ribs and a " peculiar glazed deposit" on the 

 interior of the aperture (Ad., op. cit.) The animal has not been 

 examined thoroughly, and nothing is known of its dentition. 

 Until further ^information is brought forward it can hardly be 

 united with the genus Patina, as has been done by Jeffreys.* 



HELCIONISCUS, uora. subg. prov. 



Shell solid, heavy, moderately elevated, with a subcentral 

 inconspicuous apex. Cordon interrupted in front, ending ab- 

 ruptly on each side, at the anterior ends of the adductor. Sides 

 of foot and mantle edo-e smooth. Teeth ^ The inner 



° 3(2—1.1—2)3 



uncinus hardly raised above the level of the ribbon, and second 

 lateral largest, as in Patinella. 



Type Helcioniscus variegatus, Dall. ex Rve. Plate 16, fig. 27. 



Patella variegata, Rve. Conch. Syst. ii, pi. 136, f. 1. Conch. 

 Icon. pi. xvi, fig. 36, a, b, c. {Hah. Australia, in error?) 

 Savigny, Egypt, pi. 1, f. 3. Fischer, Journ. de Conchyl. 

 X, April, 1870, p. 167, No. 42. (Suez.) 



Soft parts ; foot large, oval, thin, sole lead-colored, sides 

 smooth, yellowish ; mantle dotted with brown and with brown 



* Stoliczka (Pal. Indica, ii, p. 321) proposes to arrange the fossil lim- 

 pets under Helcion, Nacella, Tectwa and Patella, according to the 

 external characters of the shell. As it is absolutely impossible to deter- 

 mine the true affinities of these remains, from the characters preserved 

 in a fossil state, such a plan is doubtfully expedient, as it implies a knowl- 

 edge which is not attainable. It would be preferable, perhaps, to refer 

 all the fossil forms to Patella, with a query, rather than to give names 

 implying the existence of characters which can never be determined. 

 Paleontology, in a great measure, does not admit the prosecution of the 

 only satisfactory methods of zoological research, and hence must ever 

 remain far behind them. 



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