1917. 1 E. W. Vredenburg : On Pleurotoma congener. 317 



be entirely concealed by the posterior margin of the following 

 whorl. The interval between these two anterior threads may 

 carry an additional fine revolving line. Two more or less distinct 

 revolving lines may bound the sinus ridge externally to its two 

 main threads, one on either side. The sinus ridge is crenulated at 

 close and even intervals by short straight ribs, practically vertical 

 or very slightly oblique and anteriorly retrocurrent, swelling into 

 blunt granules across the two main spiral ridges. The circum- 

 sutural ridge is also denticulated, but at less regular intervals, by 

 thickened lines of growth. The course of the lines of growth is 

 steeply antecurrent or practically normal to the posterior suture, 

 antecurrent at about 45° to the anterior suture, strongly retro- 

 current from either side to the sinus ridge. 



The broad body-whorl measures from nearly five-eighths to 

 nearly two-thirds of the total height. Anteriorly to the sinus- 

 ridge it contracts with a hemispherical or somewhat flattened con- 

 vexity, connected by a rather broad and rather shallow concavity 

 with the rather short terminal stem, which is rather bluntly trun- 

 cated and very distinctly dorsally deflected at its extremity. The 

 ornaments of the last spire-whorl are continued upon the corres- 

 ponding portion of the body-whorl, with a tendency towards an 

 increase in the number of minute spiral raised lines of the lowest 

 order. In those specimens in which the spire-whorls exhibit two 

 main spiral threads anteriorly to the sinus ridge, the convexity of 

 the base, anteriorly to the level of the suture, carries two more 

 main spiral threads. In those specimens in which there is only 

 one main thread clearly visible on the anterior part of the spire- 

 whorls, the next one, concealed by the suture, becomes clearly 

 disclosed at its termination, and is followed on the anterior con- 

 vexity by only one more main thread. Consequently, anteriorly 

 to the sinus ridge, the convex portion of the body-whorl carries 

 three or four main spiral threads or keels conspicuously granulated 

 at their intersections with the raised lines of growth. From one 

 to three fine spiral raised lines are observed in each of the inter- 

 ^ vals between these granulated keels. Another similar granulated 

 keel occurs at the junction of the anterior concavity and of the 

 terminal stem. A number of thin raised spiral lines, either all of 

 one size or else more or less regularly alternating, decorate the 

 concavity. The terminal stem carries numerous spiral threads at 

 first alternating in three sizes and afterwards, more or less regu- 

 larly in two, as far as the zone of accretions of the terminal trun- 

 cation ; the threads of the first order being at first distinctly granu- 

 lated and but slightly inferior in thickness to the above-described 

 main granulated keels of the anterior part of the body- whorl, and 

 afterwards gradually decreasing anteriorly while the granulations 

 become fainter. The terminal zone of accretions which causes the 

 terminal dorsal deflection of the stem carries very fine, rather blunt 

 spiral lines crossed at irregular intervals by the somewhat rugose 

 accretions. The lines of growth become vertical at the junction of 

 the convex and concave portions of the base, and maintain that 



