MOLLTTSCA OE THE ' CHALLENGER EXPEDITION. 87 



The specimens before me seem to be quite distinct from all the 

 other American species of Pinnotheres. From P. ostreum they 

 differ in the non-dilated penultimate joint of the first pair of 

 ambulatory legs, and in the much shorter dactyli of the second 

 ambulatory legs ; from P. maculattts in the form of the carapace 

 and the much shorter dactyli of the fifth ambulatory legs ; from 

 P. Querinii and P. hirtimanus, M.-Edwards, both from Cuba, in 

 the non-spatulate dactyl of the outer maxillipedes ; and from the 

 latter also in the non-ciliated inferior margins of the chela?. 

 P. margarita, Smith, from the Bay of Panama, is at once distin- 

 guished by its pubescent carapace and legs • P. IWhodomi, Smith, 

 from the same locality, by the form of the merus joint of the 

 outer maxillipedes and the proportionate leDgth of the dactyli of 

 the ambulatory legs. 



Mollusca oe H.M.S. ' Challenger ' Expedition. — Part Y. 

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



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

 [Eead April 15, 1880.] 



Families and Genera. 



Solenoconchia, viz. Siphodentalium honohduen&e (omitted). 

 Teochid-S), viz. Trochus (omitted). 

 HETEROPHROSYNiDiE*, viz. Jeffreysia, 

 Litoeinid^e, viz. Echinella, Lacuna, and Fossarus. 

 Cerithiid^i, viz. Cerithium, Litiopa, and Cerithiopsis. 



This group of shells includes some inadvertently omitted before, 

 two families sparingly and unsatisfactorily represented, and a 

 considerable number of Cerithiidse. They are chiefly from shallow- 

 water, and need little remark. I may therefore take the op- 

 portunity to say a word regarding the identification of ' Chal- 

 lenger' specimens with known species, a work already embracing 

 over six hundred species, and now nearly completed. This work 

 of identification, with the labour of hunting up references, even 

 though no such exhaustive citation of authors as is suitable for a 

 monograph of a limited group has been attempted, has been a 



* This formidable name of Clerk's is adopted here in preference to Cray's 

 name of BissoellidcB, in deference to the arguments of Dr. Cwyn Jeffreys, who 

 assures me, 1st, that Clerk's name has priority (of which I am not quite con- 

 Tinced) ; and, 2nd, that Eissoella, Gray, was founded on Pyramis glabrus (sic), 

 Brown, " which is evidently an Odostomia." 



