EEPOKT ON THE GASTEROPODA. 129 



is broad, thick, sballowly excavated, with a slight external median horizontal tooth or 

 ridge; the edge is reverted and closely appressed. Operculum 1 small, thin, calcareous, 

 flat, convex on the inside, where it shows 7^ whorls ; the last whorl close to its end 

 begins suddenly to enlarge. Teeth distinctively those of the genus (see Troschel, Gebiss, 

 &c, vol. ii. p. 213, pi. xx; fig. 7), there being endless rows of innumerable minute 

 crooked uncini, with several (probably eleven) hooked and serrated central rasps, but 

 in their confused dried-up condition it was impossible more minutely to identify 

 them. H. 0'27 in. B. 0-25, least 0*23. Penultimate whorl, 0-09. Mouth, height 0-13, 

 breadth 0-12. 



Collonia marginata, Lam. (British Museum), in colour and form more than any other resembles 

 this ; but that is lirated, is rounded on the base, lacks the little tubercle in the middle of the flattened 

 and expanded pillar, is toothed on the outer lip, and has not the angulation in the middle of the 

 whorls. 



It has been impossible for me to quote for this species Mr Dall, who, in the " Blake " Mollusca 

 (Bull. Mus. Comp. Zool., Cambridge, U.S.A., 1881, vol. ix. p. 48) suggests the probability of his new 

 species Lcptothyra albida being the same as Turbo (Collonia) induta, Wats.; and still less can I quote 

 Professor Verrill, who in his Mollusca of New England (Trans. Conn. Acad., vol. vi. pt. 1, May 1884, 

 p. 197) asserts their identity. But in point of fact the two species have never been actually compared, 

 and all that is certain is the identity of the Cape Hatteras (142 fathoms) species with Mr DalFs from 

 the Gulf of Mexico and Havana (125 to 1002 fathoms). 



Apart from this difficulty, however, is one connected with the genus Leptothyra, Carp., to which 

 Mr Dall attributes his species. That is a genus very little known, but (teste Dall loc. cit., p. 49) is 

 characterised by a tooth on the pillar, and (teste Tryon, Struct. Conch., vol. ii. p. 312) by a corneous 

 operculum, fixing its place as a Trochus. Now, the Challenger species has a calcareous operculum, 

 and is a Turbo. But then, again, Mr Dall speaks of his species as having " the usual solid shelly 

 operculum," and this remark (while opposed to the description of Turbo (Collonia) induta, Wats., 

 whose operculum is small and thin) harmonises with Dr Carpenter's note regarding Leptonyx 

 sanguineus, " Linn." (see Brit. Assoc. Eeport, 1863, Moll., West Coast America, p. 652, No. 269 — that 

 species as found in California, not in the Mediterranean, being, as I understand, the type of Leptothyra, 

 Carp.), to the effect that the operculum has " horny and shelly layers." Being unable myself to 

 reconcile all these points, I must be satisfied to call attention to them as needing elucidation. 



As to the Challenger shell, it is of course obvious that the minute tooth or small tubercle on 

 the middle of the exterior flattened pillar-lip, neither edge of which it reaches at all, is a feature dis- 

 tinguishing the shell from an ordinary Collonia, and would be more than enough in the opinion of 

 many for the creation of a new genus, but one who regards such creations as a very great evil is 

 compelled to avoid them wherever it is possible, and Collonia is too small a group to need 

 breaking up. 



1 The solitary specimen of this operculum has been lost, it is^believed, in the hands of the artist engaged on 

 the shell. 



(ZOOL. CHALL. EXP. — PART XLII. — 1885.)} Tt 17 



