494 
MR. H. N.’ RIDLEY ON THE 
umbilicated than the shells figured by Reeve* and Fischer f, and 
also differ in form, being wider at the base and more shortly 
conical. 
Fischer has already pointed out that the localities of Reeve 
and Lamarck, Swan River and Mauritius, are probably incorrect. 
33. Trochus (Eutrochus) gemmosus, Reeve. 
This I believe, as in the case of the preceding species, is another 
instance of a wrong locality (Philippine Islands) assigned by 
Reeve. 
Two specimens from Fernando Noronha agree in every minute 
detail with the types in the British Museum, and, as the sculpture 
and lineations are so remarkable, the identity is beyond doubt. 
The umbilicus, which is as large as that of T. jujubinus , at once 
distinguishes this species from T. nobilis, with which Philippi X 
questioned its relationship. The type of Riitroclius was named 
R. perspectivus by A. Adams ; but as that name was previously 
used by Koch for another species belonging to the same group, 
Pilsbury has renamed it R. Adamsi. 
34. Fissurella cancellata, Soiverbg. 
Fissurella cancellata, Sowerby, Concli. III. sp. 38, pi. 72. f. 29; 
Hah. West Indies, Honduras. 
With this species I would unite Riss. siiffusa , Reeve, and R. 
lentiginosa, Reeve. A third species of the same author, R. cegis , 
is also very similar, but the form is a little more elongate and the 
radiating riblets are squamose at the points of intersection with 
the concentric line. 
35. Fissurella alternata, Sag. 
Fissurella alternata, Say, Journ. Acad. N. Sci. Philad. 1822, vol. ii. 
p. 224 ; Reeve, Con. Icon. pi. xii. f. 84 (probably). 
Fissurella larva, Reeve, l. c. f. 98. 
Fissurella Dysoni, Reeve, l. c. f. 86. 
Hab. Maryland, &c. (Sag) ; Bermuda, St. Johns, Honduras 
(Brit. Mus.). 
The sculpture of the three above-named forms is essentially 
the same and the character of the orifice is similar, and all have 
* Con. Icon., Zizyphinus, pi. 2. fig. 12. 
+ Kiener’s Coq. Yiv., Trochus, pi. 18. f. 2. 
J Conch.-Cab., Trochus, p. 8G. 
