MOLLUSCA OF THE * CHALLENGER ' EXPEDITION. 451 



a very slight contraction from this point to the inferior suture ; 

 the last whorl is tumid, but short, with a sloping shoulder, a much 

 blunter angulation, a marked contraction from this point, a very- 

 blunt angulation defining the base, which contracts a good deal 

 and suddenly, and which on the right side is prolonged into 

 the conical, triangular-shaped, blunt- though small- pointed 

 snout. Suture linear and almost invisible, but well defined by the 

 angulation at which the whorls meet, and also by the change of 

 colour where the inferior whorl laps up on the one above it, which 

 produces a pseudo-margination. Mouth large and irregularly 

 semicircular, angulated above, and ending in a distinct open 

 canal below. Outer lip excessively thin, slightly patulous below, 

 but not at all above ; it leaves the body at a right angle, and 

 advances across the sinus-area in a perfectly straight line; it is 

 angulated at the keel, from which point it curves very regularly, 

 till towards the edge of the canal it becomes concave and finally 

 straight ; round the front of the canal it is not in the least patu- 

 lous : its edge forms a semicircular curve with a high shoulder, 

 between which and the body lies the large, broad, open, rounded 

 sinus. Inner lip, which, though very narrow, is continued to the 

 point of the pillar, is cut into the substance of the shell, and is 

 defined by a slight raised margin beyond it ; the line across the 

 body is very short, and joins the pillar at a very obtuse angle. 

 The pillar is very long and straight, and is cut off in front with a 

 very gradually oblique, thin, twisted edge. H. 1*04. B. 0*52. 

 Penultimate whorl, height 02. Mouth, height 059, breadth 0*3. 

 This is a species of the most singular beauty and delicacy, like 

 nothing known to me. 



49. Pleurotoma (Thesbia) brtchia, n. sp. (/3py^ts, from the 

 depths.) 



St. 106. August 26, 1873. Lat. 1° 47' N., long. 24° 26' W. 

 Mid- Atlantic. Bottom temperature 36 c, 6. 1850 fms. Gldbige- 

 rina-ooze. 



Animal. — In colour pale buff" with a greenish liver. The mantle 

 is prominent, thin, made up of separate, but connected, threads 

 like a fringe, with a denticulated margin. From within it to the 

 left a great fold of flesh projects, whose drawn-together edges 

 form the anterior siphon ; this fold is an extension of the inner 

 side of the mantle close within its edge, which edge expands into 

 a flap to enclose this siphon. On the right the mantle is drawn 

 back and expanded, so as to form an imperfect open channel cor- 



