NO. 1264. ILLUSTRATIONS OF AMERICAN SHELLS— BALL. 533 
the first whorl and three on the sub.'^equent whorls in front of the 
suture, and on the last whorl there are nine or ten diminishing in size 
forward, from the periphery to the end of the canal, but of the same 
general type; they are crossed only b}" fine incremental lines. Lon. of 
shell 4.5; max. diam. 2.5 mm. 
Dredged by the U. S. Fish Commission steamer Albah'oss in the straits 
of Magellan at .station 2777, in 20 fathoms, gravel. U.S.N.M., 9G190. 
This ver}' remarkable little shell has the general form of yiW Anaclds^ 
but the sculpture is more like some of the species of Trophon^ while 
the pale yellow^ operculum is also much like that of Trophon. If it 
were not that the torsion of the nuclear and subsequent whorls is in 
opposite directions, the shell might be taken for a \evy minute reversed 
Troplwn or ZTwiialjnnx. It may be that the two specimens which were 
obtained and which a.gree perfectly are immature, and that the aper- 
ture may be Urate when fully grown, but there is no indication in the 
shell to suggest it. 
Genus TROPHON Montfort. 
The genus Trophon^ founded on the Patagonian species ge'vet^siamis 
of Pallas, belongs to the Purpuroid group of Murices with Ocinehra 
and Eupleura. The larger species show the peculiar rotating impi-ints 
on the proximal face of the operculum, which are usually regarded as 
characteristic of Purimra. The smaller species with thin opercula do 
not always develop these markings. The nucleus of the operculum is 
on the outer side between the middle and the lower angle, exactly as 
in some Purpuras, with a callus around the inner margin. The nuclear 
whorls of Troplum are small and either inflated or, by reason of a 
small carina, flattened above and tilted, so that the plane of the first 
whorl forms an angle with that of the succeeding whorls. This is 
sometimes .so marked that at first sight it appears as if the nucleus was 
reversed as in PyrcmiideUidcE^ but a careful examination shows that 
this is not the case. Mo.st .species have the nepionic whorls immedi- 
ately following the nucleus sculptured, and often cancellated, whether 
the remainder of the whorls are so or not, indicating the derivation of 
the group from a cancellated, or, at least, a sculptured ancestral type. 
The typical Trophons are chiefly austral and have a rather character- 
istic type of form and sculpture. The boreal forms show more variety 
and have developed several types among themselves, all diflerent from 
the antarctic group, and which I therefore separate as a genus, Boreo- 
trop>h(m (Fischer, 1884). This genus, again, is divisible into several 
sections characterized by their sculpture. The typical Boreotnplion 
has lamellar varices, the spiral sculpture is absent or feeble, and the 
operculum is elongated and narrow with the nucleus apical, and no 
purpuroid markings on the inner face. The section TrophomypsU 
(B., D., and D., 1882) has spiral sculpture quite emphatic, and .some- 
