ball: mollusca and brachiopoda. 257 



culum subovate, acute in front, with a medial thickened rib on the inner face, the 

 area 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 : 



Irenosyrinx Dall, nov., 190S. Shell large, thin, fusiform white, with a keel 

 at the shoulder ; sculpture feeble, wholly spiral ; anal sulcus wide, shallow, nearer 

 the shoulder than tlie suture ; axis pervious, aperture and canal longer than tiie 

 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 concentric 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 Turris {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 tlie operculum remains permanently paucispiral. 



CocHLESPiRA 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 fascicle sepa- 

 rated from the suture by a beaded ridge, the outer margin of the fasciole not ele- 

 vated. Type Pleurotoma crista ta Conrad. Oligocene fossil. 



This group is extremely close to Aucistrasyriux Dall, 18S1, 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. 



Stetr.\xis 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. 



Calliotectum Dall, 1889. Shell with a dark vernicose pcriostracum, 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 group 

 appeared in the original publication as a subdivision of Mangilia instead of 

 Pleurotoma. 



In the Mangiliinao the following groups have species referred to in this paper: 



VOL. XLIII. — NO. 6 17 



