88 



lEIDINA. 



GEJS^US PLATIKIS/ 



I. SUBGENUS IRIDINA. 



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OBLONG. 



Spekii.' Woodxvard. 



OBOVATE. 



""*ovata. Swain. Woodward. 

 Irid. exotica. Children. 

 Irid. spendida. Chenu. 

 Pleiodon Macmurtriei. Con. 

 Pleiodon ovata. Con. Chenu. 



*Leaii.^ Sow. 



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ARCUATE. 



*exotica. iam. Desh.^ Pot. Chenu. 

 Irid. striata. Swain. Woodward. 

 Irid. elongata. Sow. 



Species Unhioivn to me. 



Iridina valeus.° Parr. 

 Iridina solida. Anton. 

 Iridina Welwitclaii. More. 



' Genus Platiris (nobis), nxarv?, latus ; epij, iris. Testa sequivalvis, late transversa; impressiones 

 musculares grandes; cardo longus, linearis; ligamentum externum. 



^ When Lamarck established his genus Iridina, he had seen but a single species, and of that only 

 one individual, which is figured in the Encyclop. Methodique, PI. 204. Other species have been since 

 referred to his genus, which do not seem to me to fulfil the conditions of his generic diagnosis. The 

 phrase "cardo per longitudinem tuberculosus, subcrenatus," is by no means descriptive of the hinge 

 belonging to the species just alluded to, which has the hinge smooth, or very slightly tuberculate. The 

 figure in the Encyclopedie, and that of Blainville (PI. 66, Fig. 3), represent the same individual, and 

 exhibit a character of hinge resembling in some measure that of an Area. A second species, apparently 

 agreeing with Lamarck's generic description, has been observed and described by Swainson, under the 

 name of Iridina ovata (Phil. Mag., vol. Ixi.) ; and it has also been described by Mr. Children under the 

 name of I. exotica {BrancWs Journ., vol. xv.). The specimen described in Brande^s Journal is now in 

 the British Museum, and that accurate naturalist. Dr. John Edward Graj^, who is one of the officers of 

 that noble institution, informs me that he thinks it is identical with the shell ui^on which Mr. Conrad has 

 lately proposed to form a new genus, Pleiodon. Under these circumstances, it seems to me necessary to 

 separate those shells having a crenulated hinge (which are true Iridinae), from those having the hinge 

 smooth, or very slightly tuherculated. I therefore arrange the Iridina rubens, Nilotica, &c., in a new 

 subgenus, for which I propose the name of Spatha. In an intemperate note by Mr. Conrad, on the cover 

 of No. 11 of his Monograj^hy, he says that I refer P. 3facmurtriei to Iridina ovata, because Dr. Gray 

 thinks them identical; and further says this "must be a wilful error" on my part! But this irritable 

 remark cannot alter the fact. It is identical. Mr. Swainson {Malacology, p. 286) says "the name of 

 Pleiodon cannot be substituted for that of Iridina, as applied to the tjqjical species." 



Ferussac says that Humphrey, in his Catalogue (MSS.?), made a genus (Scapha) for an Iridina, and 

 that the '■'■mutel, D'Adanson," is certainly the same {Mem. de I'Hist. Nat. cle Paris, v. i. p. 362). 



^ This has so much the characteristic of ovata that I should not be surprised if it proved eventually 

 to be a well-marked variety of that species. 



* Mr. Sowerby very kindly presented me with a specimen under this name. It looks to me like a 

 yoimg I. ovata, and I have little doubt but that it will prove to be such. 



^ M. Deshayes gives the Nilotica as a synonym to this species, but I think it is distinct. 



' From Africa, in Jay^s Cat. 



