MELVILL— MAEINE MOLLUSCA. 127 



Allied to P. corallinoides, d'Orb., from tlie Capo dc Vcrdes, and with wliicli, a larger 

 and very different species, it has been sometimes unwarrantably confounded. 



406. Pecten nux, Reeve. 



Loc. Cargados Carajos : Station B 20, 28 fathoms, coarse coral-rubble. 

 Saya de Malha Banks : Station C 15, 55 fathoms, similar bottom. 



407. Pecten pallium, L. 

 Loc. Chagos Archipelago. 



Small and ])oor examples only of this most select and brilliant species. 



408. Pecten perfectus, sp. nov. (Plate 5. hg. 15.) 



P. testa compressa, sequivali, pulchre miniata, hie illic albo ct uigro couspersa, radiis 

 albis, prsecipue marginem apud ventralem, obscuris decorata, auriculis valde in- 

 aequalibus, postica parva, obliquissima, antica decem-costata, breviter squamata, 

 superflcie omni in valva utraque, longitudinaliter arctissime et delicate tenuicostata ; 

 costis fere 55, minute squamulosis, fere regularibus ; iuterstitiis planatis, nitidis. 

 Alt. 25, lat. 23, diam. 6 mm. 



Loc. Chagos Archipelago : Peros Banhos, Diainant, 16 fathoms. 



This pretty Pecten seems most akin to the coarser P. irregularis, Sowb., wliich occurs 

 in the same region and is widely distributed in the Indian Ocean. It differs in its far 

 greater regularity of longitudinal costue, these being about 55 in number, close and 

 fine-set, the interstices being smooth and shining ; the ribs themselves are delicately 

 scaly. The colour is scarlet-crimson, here and there flecked with white suffusion 

 bordered by black spotting ; around the ventral margin are five or six white rays, 

 becoming soon evanescent. I am much indebted to Mr. G. B. Sowerby for his opinion 

 concerning this interesting species. 



409. Pecten plica (L.). 



Loc. Amirantes : Stations P 5, 32 fatlioms, sandy ; E 9, 34 fathoms, Polyzoa and shell- 

 rubble. 



410. Pecten i^orphyreus, Chemn. 



Log. Cai'gados Carajos : Station B 14, 30 fathoms, on shell-rubble. 



Amirantes : Stations E 5, 32 fathoms, sandy ; E 15, 20-25 fathoms, E 21, 



30 fathoms, in both stations amidst Malimeda and other calcareous Algse. 

 Chagos Archipelago : Diego Garcia, Barachois Maurice. 

 P. porphyreus, Chemn., is probably an outlying, squamosely ribbed form of the fairly 

 smooth and large P. senatorius, Gmel., so abundant an inhabitant of the Arabian Sea 

 further north. It is, at best, an extremely variable species, and it is a question whether 

 the very fine P. gloriosus, Beeve, and crassicostatus, Sowb., had not best be treated as 

 synonymic. The distribution of the typical form is wide, extending to Japan : the 

 varieties are more or less restricted in range. 



