DALL: MOLLUSCA AND BRACHIOPODA. 201 
culum subovate, acute in front, with a medial thickened rib on the inner face, the 
arca of attachment small, the nucleus apical. Type Pleurotoma verrilli Dall. 
This group is chiefly Atlantic in its distribution, and as at first used comprised 
Some species which I now separate as follows : 
Irenosyrınx Dall, nov., 1908. Shell large, thin, fusiform white, with a keel 
ab the shoulder; sculpture feeble, wholly spiral ; anal suleus wide, shallow, nearer 
the shoulder than the suture; axis pervious, aperture and canal longer than the 
Spire; outer lip produced, thin, simple ; canal elongate, pillar obliquely truncate ; 
operculum in the young paucispiral, later the paucispiral nucleus is surrounded 
by concentric additions, leaving the nucleus subcentral, or a little anterior and to 
the right, in an elliptical concentrie operculum without internal rib, with a large 
area of adhesion, and an outline in general like the operculum of Buccinum. 
Type Pleurotoma (Leucosyrinx) goodei Dall, 
This group seems rather characteristic of the eastern Pacific, usually in rather 
deep water. The Zwrris (Aforia) circinata Dall, from the North Pacific, has 
much the same type of shell, though of a brown color, but has the operculum 
narrow with an apical nucleus, and, in the adult, a prominent and singular chan- 
nel in the anterior part of the outer lip. Irenosyrinx is doubtless a modification 
of the type Steiraxis, in which the operculum remains permanently paucispiral. 
Cocutmsrira Conrad, 1865. Shell moderate in size, with a subacute, few 
Whorled, glassy nucleus, elongated slender, straight canal, the whorls tabulated 
by a sharp recurved spinose or beaded keel, between which and the suture the 
Surface is concave, nearly smooth; anal sulcus deep, narrow, the fasciole sepa- 
rated from the suture by a beaded ridge, the outer margin of the fasciole not ele- 
vated. Type Pleurotoma cristata Conrad. Oligocene fossil. 
This group is extremely close to Ancistrosyrinx Dall, 1881, the latter differing 
only by having the anal sulcus at the suture, with no intervening ridge, while the 
Outer margin of the fasciole has an elevated lamella between which and the reflected 
keel at the shoulder there is an excavated channel. These differences hold good 
between the Oligocene and the recent forms, so far known, without exception. 
The recent forms have an operculum like that of Leucosyrinx. 
Sterraxis Dall, 1895. Shell resembling Irenosyrinx, but with stronger sculp- 
ture and with a paucispiral operculum, bearing such a relation to the normal 
Species of Turris as Mohnia bears to Chrysodomus. 
Carroreorum Dall, 1889. Shell with a dark vernicose periostracum, no 
differentiated canal, anal sulcus or fasciole ; axially ribbed, pillar thin, twisted ; 
axis impervious ; outer lip simple, arcuate, thin, not internally lirate ; operculum 
like that of Fusinus, but arcuate; animal blind, without radula or poison gland. 
Type C. vernicosum Dall. 
By a misplacement of a sheet of the MS., not detected at the time, this grou p 
appeared in the original publication as a subdivision of Mangilia instead of 
Pleurotoma. 
In the Mangiliinae the following groups have species referred to in this paper: 
VOL. XLIII. — NO. 6 1 
