278 AMERICAN JOURNAL 



maculae on the upper edge corresponding to the rays of the 

 shell, edge somewhat irregular, resembling the shell margin, 

 apparently quite smooth, and destitute of beards or fila- 

 ments. Branchial lamell?3 large, not crowded, large and small 

 alternate!}'', terminating anteriorly on each side close to the 

 end of the adductors. Hood smooth, thin, very varicose, as 

 is the thin inner part of the mantle. Head prominent, tentacles 

 short, pointed, slender, bases somewhat swollen, with the eyes on 

 the upper posterior portions. Muzzle short, transversely oval, 

 without a frill, disk slightly granulose, especially at the edges, 

 mouth large, rounded, buccal lips conspicuous ; jaw thin, pale 

 yellow, edge somewhat irregular from use ; anal and infra-anal 

 papillae close together on the right-hand side, long, slender, cyl- 

 indrical ; anal orifice simple, not papillose internally, infra-anal 

 bifid at tip, renal smaller than the others on the left side of anal 

 papilla. Intestine full of red matter, probably from corallines; 

 faeces expelled in cylindrical pellets. Crop moderate, a third as 

 long as the body. No " capito-pedal " orifices to be detected 

 iuternally, externally, or by injections. Radula coiled near the 



buccal mass, on the inferior surface of the liver. Formula, 







Ja-f3^-ri~i4+ij3' 



Locality, Red Sea and Gulf of Akaba, Smithsonian Cabinet. 



The peculiarities of the shell of Heleion render it probable 

 that it differs generically from the group under consideration, 

 although the bvanchiiB exhibit points ;of resemblance, and I am 

 inclined to believe that such of the species, now included under 

 SeuteUina, as cannot be affiliated with the Acmceidce, may find a 

 resting-place in the genus Heleion. 



The Helcionisci are tropical forms most nearly allied to Pa- 

 tinella. 



Helcioniscus rota, Rve. Plate 16, fig. 28. 



Patella rota, Chemn. Conchyl., Cab. x, p. 330, pi. 168, fig. 

 1619. Rve Conch. Icon., pi. xvii, 39 a, b, c. ? = H. 

 variegata, Rve., ante. 



Animal in every respect resembling the last. The teeth, which 

 are figured in a slightly diff'erent position from those of ^. varie- 

 gatus, Rve., do not exhibit any differences of value. I am in- 

 clined to think that they may be identical, in which case, the 

 species will take the name of II. rota, which has priority over 

 variegatus. The species before me is undoubtedly the former. 



Hab. Madagascar, Caleb Cooke. 



Helcioniscus (?) argentatus. Gray, sp. 



Patella argentata, Gray, Moll. Beechey's Voyage, p. 148, pi. 

 39,- f. 7. Gould, Expl. Exp. Moll., p. 345, pi. 29, f. 451. 



