EEPOET ON THE GASTEROPODA. 299 



upper and lower suture ; there is besides a very faint approach to a carination in the middle 

 of each whorl ; they are of rapid but regular increase ; the last one is long and a very 

 little tumid ; contracting on the base very gradually to the one-sided, longish, smallish, 

 pointed snout. Suture fine but well marked, oblique. Mouth a very long and narrow 

 oval, pointed above and below, oblique. Outer lip thin, regularly curved. The sinus is 

 very broad, open and deep, and lies quite up to the suture. Inner lip : a very thin glaze 

 spreads narrowly on the body ; it is concave in form throughout ; round the base of the 

 pillar there is a very slight tumidity, the front of the pillar is twisted and fined away 

 with a rounded and slightly prominent edge. H. 2 - 65 in. B. 0"87. Penultimate whorl, 

 height 0'55. Breadth of first remaining whorl, 0-06. Mouth, height 1/22, breadth 0'43. 



This is a very remarkable form, not at all like a Pleurotoma. Pleurotoma tomata, Dillw., is the 

 form which most resembles it, but is much broader, with a more tumid body-whorl, a flatter-sided 

 spire, and a much longer snout. There is only one specimen, and the outer lip, beset by one of the 

 deep sea Actinias, is badly broken. I have given the size of the first remaining whorl of the apex, as 

 only by such means is a common starting-point established for comparison with any other specimen. 



27. Pleurotoma (Genota) didyma, 1 Watson (PI. XXII. fig. 5). 



Pleurotoma {Genota) didyma, Watson, Prelim. Report, pt. 8, Journ. Linn. Soc. Lond., voL xv. p. 404. 



Station 23. March 15, 1873. Lat. 18° 24' N., long. 63° 28' W. Off Sombrero Island, 

 West Indies. 450 fathoms. Pteropod ooze. 



Shell. — High, mitriform, biconical, ribbed, and with spiral threads ; the spire sub- 

 scalar ; the mouth narrow ; the sinus very slight. Sculpture : Longitudinals — the whorls 

 are crossed by eleven oblique, rather strong, but narrow hunchy ribs, with broad open 

 furrows between ; these ribs and furrows tend to disappear on the last whorl, and they die 

 out on the base ; there are also very fine, close, hair-like lines of growth. Spirals — the 

 suture is not quite closely marginated below by a rather slight thread ; the sinus-area 

 below this is formed by a little open concave furrow ; below this is a series of about 20 

 (on the penultimate whorl about 5) pretty equal rounded threads and furrows — the first 

 is weaker than the rest ; the second occupies the edge of the shoulder, and marks the 

 angulation of the whorls, there rising (as does also the next thread below) into special 

 prominence in crossing the ribs ; towards the extreme point of the shell, beyond the 

 threads above referred to, are three or four smaller closely crowded threads. Colour 

 white. Spire high, conical, scalar. Apex broken (but probably blunt and Mangelia- 

 like). Whorls below the embryonic ones 6-7, of slow and regular increase, short and 

 broad, high but small shouldered, prominent above, and a little contracted below ; the 

 last contracts from the keel and forms a perfect cone on to the extreme point. Month 



1 d!8u/to{% doubtful. 



