300 THE VOYAGE OF H.M.S. CHALLENGER. 



(Dunker), Macassar and China (Reeve). In tlie " Alert " Report I forgot to mention 

 that in addition to the diflerence of colouring the typical form also presents a difference 

 in outline. The auricles are certainly larger than in either of the varieties, and the 

 sides are more spreading or fan-like. This variation, however, is approached by one of 

 the specimens of var. hunlioltzi in the British Museum, and I have little doubt that had 

 I a large series for examination I should find many intermediate forms, and should also 

 probably observe tliat each variet}^ as a rule maintains its special shape. 



Pecten senatoi^ius (Gmelin), var. 



Odrea senatoria, Gmelin, Syst. Nat., p. 3327. 



Pecten senatorius, Sowerby, Thes. Conch., vol. i. p. 74, pi. xvii. fig. 151, and pi. xviii. figs. 



188-192. 

 Pecten senatorius, Eeeve, Conch. Icon., vol. viii. pi. xxi. fig. 81. 



Habitat. — Stations 203 and 208, Philippine Islands, in 20 and 18 fathoms. 



The single specimen from Station 208 and two from 203 differ from each other in 

 colour and also somewhat in sculpture. Both forms are also very unlike the Pecten 

 seJiatorius, as figured in Reeve's work as regards colour, but after careful consideration 

 and comparison I do not think it advisable to separate them. The former specimen has 

 more the general appearance of Pecten layardi, Reeve, the other two more resembling 

 Pecten rugosus of Sowerby. There is a large group of species which requires careful 

 investigation, and which probably could be considerably reduced in number. It 

 comprises Pecten senatorius, Pecten criientatus, Reeve, Pecten gloriosus, Reeve, Pecten 

 crassicostatus, Sowerby, Pecten nobilis, Reeve, Pecten layardi. Reeve, Pecten cristidaris, 

 Adams and Reeve, Pecten rugosus, Sowerby, Pecten triradiatus. Reeve, Pecten 

 testudineus, Reeve, Pecten cloactus. Reeve, Pecten miniaceus, (Lamk.) Sowerby, Pecten 

 jJseudoUma, Sowerby, Pecten hlandus, Reeve, Pecten fricatus. Reeve, Pecten reticulatus, 

 Reeve, and Pecten saniosus. Reeve. The small forms may possibly be but young shells 

 of the larger ones, for we do not know the limits in size of many of the exotic species. 



Pecten corallinoides, d'Orbigny. 



Pecten corallinoides, d'Orbigny, in Webb and Bertholot's Hist. Nat. Canaries, voL ii. pt. 3. 



p. 102, pi. vii. figs. 20-22. 

 Pecten corallinoides, Sowerby, Thes. Conch., vol. ii. p. 65, pi. xii. figs. 3, 4. 



Habitat. — St. Vincent, Cape Verde Islands, in 7 to 20 fathoms ; and Teuerife, in 

 70 fathoms (Challenger) ; Canary Islands (d'Orbigny). 



The shells of this species, of Pecten noduliferns, Sowerby, and Pecten nodosus, 

 Linn., are very much alike, and, what would not be expected, a greater similarity exists 



