532 PROCEEDINGS OF THE NATIONAL MUSEUM. 
MUREX (PTEROPURPURA) CARPENTERI Dall. 
Plate XXXIV, fig. 9. 
PUronotU!^ carpcrUerl Dall, Nautilus, XII, No. 12, April, 1899, p. 138. 
Farallonos T.slands, California, south to the vicinity of San Diogo, 
California, in 15 to 60 fathom.s. U.S.N.M., 122596. 
The shell i,s of a somewhat livid pale brown, pinkish toward the 
apex and white around the aperture. The surface, except of the 
nuclear whorls and the anterior faces of the varices, is smooth. The 
genus resembles Pterorhytls Conrad very much, except in the absence 
of the spur on the outer margin of the aperture. There are three 
series of continent varices. 
This subgenus was indicated by Jousseaume, in 1880; the name 
Pkronotus Swainson, is preoccupied by Gray, in Reptilia. In 1899, 
however, Rovereto proposed for this group the name Pterymurex^ 
which is entirely unnecessary; an occurrence which shows how inad- 
visable it is to propose new names for those supposed to be preoccu- 
pied, without knowing the whole history of the names in question, 
and their synonyms. 
MUREX (PTEROPURPURA) PETRI Dall. 
Plate XXXIV, fig. 7. 
kurex ])etri Dall, Nautilus, XIV, August, 1900, No. 4, p. 37. 
San Pedro, California, in about 50 fathoms; Oldroyd. U.S.N.M., 
122553. 
This species is of a yellowish-white color, covered with finely im- 
bricated spiral threads, of which about every fourth one is slightly 
larger. The aperture is white and the varices distally recurved. 
ANTISTREPTUS, new genus. 
Shell small, having the general form of Anachis, sinistral, with a 
dextral nucleus; the operculum as in Troplion. Type, A. magellani- 
cus Dall, Straits of Magellan. 
ANTISTREPTUS MAGELLANICUS, new species. 
Shell small, porcellanous white with a straw colored periostracum, 
sinistral with a smooth polished dextral nucleus and about four subse- 
quent whorls; spire rather acute, body whorl moderately rounded; 
suture distinct; pillar straight, unarmed; canal short, rather wide, 
slightly recurved; outer lip simple, sharp; no callus on the body; sculp 
ture of strong, high, coarsely beaded spirals with narrower inter- 
spaces, the swellings or beads occurring vertically below one another 
on the several spirals giving the eU'ect of ribs; there are two spirals on 
