MOLLUSCA OE THE CHALLENGER ' EXPEDITION". 245 



Mollusca of H.M.S. ' Challengeb ' Expedition. — Part VII. 

 By tlie Eev. Eobert Boog Watson, B.A., P.B.S.E., E.L.S., &c. 



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

 [Eead December 2, 1880.] 



Families and Genera. 



PyramidelliDjE, viz. Aclis, Fenella, Dunkeria? 



Naticid^Ej viz. Natica. 



Cassidea, viz. Oniscia. 



Tritonid^e, viz. Triton, Ranella, Nassaria. 



Aclis, Lov4n. 



1. Aclis niizon, n. sp. 3. Aclis sarissa, n. sp. 



2. Aclis hyalina, n. sp. 



1. Aclis mizon, n. sp. (pelfov, rather large.) 



St. VII. p. Eeb. 10, 1873. Lat. 28° 35' N., long. 16° 5' W. 



Teneriffe. 78 fms. Coral. 



Shell. — Broadly subulate, high, conical, umbilicated, thin, 

 glassy, feebly ribbed longitudinally. Sculpttire. Longitudinals — 

 on the penultimate whorl there are about 40 feeble unequal 

 rounded riblets, which run obliquely from left to right across the 

 whorl; they die out on the last whorl, which, towards the mouth, 

 presents a slightly malleated surface ; on the upper whorls these 

 riblets are fewer but more equal and distinct, but gradually die 

 out towards the apex ; they are parted by furrows rather broader 

 than themselves ; on the base they are very feebly present ; the 

 whole surface is further covered with faint irregular hair-like 

 lines of growth. Spirals — there are a few very feeble, flatly- 

 rounded, barely raised threads on the last whorl ; these are rather 

 more distinct on the base. Tbe edge of the base is slightly and 

 hesitatingly angulated ; the lip of the umbilicus is much more 

 distinctly and sharply so. Colour thin transparent white, so as 

 to be almost glassy. Spire conical, long and fine. Apex small, 

 quite regular, and perfectly rounded, with a minute flattening 

 down of the extreme point of the first whorl, merely sufficient to 

 prevent its being prominent. Whorls 15-16, of very gradual and 

 regular increase, rounded, but the equal curve is slightly flattened 

 for the first two fifths of the whorl's height ; the base is flatly 

 rounded and rather produced. Suture linear, regular, impressed. 



