MOLLUSCA OE THE ' CHALLENGEE ' EXPEDITION. 



247 



MoLLFSCA OF H.M.S. ' Chaxlen&ee ' ExPEDiTiois^. — Part XI. 

 Bj the Eev. Eobeet Boog "Watsok, B.A., P.E.S.E., P.L.S. 



[Published by permission of the Lords Commissioners of the Treasury.] 

 [Eead December 15, 1881.] 



Pam. PLEUE,OTOMiD.a; 



(continued from Vol. XV. p. 475). 



Pletteotoma, Za7n. 



65. Pleurotoma {Drillia) exsculpta, 



n. sp. 



66. P. (D.) tholoides, n. sp. 



67. P. (-D.) amblia, n. sp. 



68. Pleurotoma {Drillia) aglaopha- 

 nes, n. sp. 



69. P. (D.) lopho'e'ssa, n. sp., with 

 var. platia. 



70. P. {Clionella) quadruplex,n.sp. 



These six species, of which the description follows, have fallen, 

 out of place from the difficulty of deciding where they should go. 

 After much and contradictory advice, they are classed here tenta- 

 tively. In all of them the style of the shell is rather that of a 

 Fleurotoma than of any thing else ; but they can hardly be said 

 to have a labral sinus. 



65. Pleueoto3ia (Dsillia) exsculpta, n. sp. 



St. 24. March 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. 

 JSTorth of Culebra Island, St. Thomas, Danish W. Indies. 390 fms . 

 Coral-mud. 



Shell. — High, narrow, conical, scalar, ribbed, with a short conical 

 base, a bluntish apex, and having the colour of thin pale flint. 

 Sculpture. Longitudinals — on the last whorl there are about 20 

 (on the first regular whorl about 12) narrow rounded ribs, which 

 originate in the suture ; just below this they rise into little rounded 

 tubercles ; at the periphery they project in larger and slightly 

 elongated tubercles, below this point they incline to the right, 

 become feebler on the base, and disappear on the snout : the lines 

 of growth are fine, but irregular and somewhat indistinct. Spirals 

 — below the suture a slight rounded thread connects the costal 

 tubercles; at the peripheral row of tubercles is a keel; feeble, 

 remote, rounded threads appear on the whole surface, becoming 



LINN. JOUEN. — ZOOLOGY, VOL. XVI. 17 



