THE FAMILY NAIADES. 



141 



GENUS PLATIRIS.t 



I. SUBGENUS IRIDINA4 







OBOVATE. 







ovata. Swain. 



s 





Iiid. exotica. Children. 



OS 



« 



Pleiodon Macmuitriei. 



02 



in 



ARCUATE. 





exotica. Lam. 



o 





Iiid. striata. Swain. 



'^^ 



' 



An. exotica. Blain. 



Con. 



II. SUBGENUS SPATHA. 



OVAL. 



*riibens.§ Lea. 



Iiid. lubens. Z)es/i. Rang. 

 An. rubens. Lam. Blain. 

 An. Clappertoni. Kcenig, in Denhani 

 and Clapperton's Journey. 



WIDE. 



*NiIotica. Z.ea. 



Irid. Nilotica. jSow. Fer. Crouch. 



Caill. 

 An. diibia'? ^osc. 

 (^ Irid. Oudnioei. Kcenig. 



t Genus Platiris (nobis), trxawc, latus ; <gjc,iris. Testa sequivalvis, late transversa ; impressiones muscu- 

 lar es grandes ; car do longus, linearis ; ligamentum externum. 



X When Lamarck established his genus Iridina, he had seen but a single species, and of that only one in- 

 dividual, 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 description. The phrase " cardo per 

 longitudinem tuberculosus, subcrenatus," is by no means descriptive of the hinge belonging to the species just 

 alluded to, which have their hinge smooth, or very slightly tuberculated. The figure in the Encyclopaedia, and 

 that of Blainville (PL 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 oi Iridina ovata (Phil. Mag. Vol. LXI.) ; and it has 

 also been described by Mr Children under the name of/, exotica, (Brande's Journ. Vol. XV. j. The specimen 

 described in Brande's Journal is now in the British Museum, and that accurate naturalist, Mr John Edward 

 Gray, who is one of the officers of that noble institution, informs me that he thinks it is identical with the shell 

 upon 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 Iridinse), from those 

 having the hinge smooth, or very slightly tuberculated. I therefore arrange the Iridina rubens, Nilotica, &c., 

 in a new subgenus, for which I propose the name of Spatha. 



§ Mr Gray informs me that Cailliaud figures a species near to this from Egypt, which is in his possession, 

 but I have not seen the shell or description. 



VI. 2 L. 



