228 Mr. E. A. Smith on the Genus Pytliina. 



centre. Nothing is known of the animal of this interesting 

 shell. 



As many as nineteen so-called species have been described 

 as belonging to this genus, or have been subsequently placed 

 in it. Some of these do not possess the remarkable sculpture 

 which characterizes the type, and differ also as regards the 

 construction of the hinge. Others agree in having divaricate 

 plications, but exhibit a widely different dentition. 



I will now proceed to discuss each of these species, and will 

 indicate the genus to which I think they should be referred. 



1. PytMna DesJiayesiana, Hinds. 



1844, Tythina Beshayesiana, Hinds, Zool. Voy. ' Sulphur/ vol. ii. p. 70, 



pi. xix. figs. 8, 9. 

 1858. PytMna Beshayesiana, H. & A. Adams, Gen. Rec. Moll. pi. cxiv. 



figs. 9, 9 a. 

 1862. FyiMna Beshayesiana, Clienu, Man. Conch, vol. ii. p. 126, fig. 603. 

 1878. PytMna Beshayesiana, Kobelt, Illust. Conchylienbuch, p. 352, 



pi. ciii. fig. 3. 



Hah. New Ireland {Hinds); also Philippine Islands 

 [Cuming^ fide Hinds). 



In my report upon the Lamellibranchiata of the ' Chal- 

 lenger' Expedition, p. 204, I have stated that the dentition 

 of this species " is exactly that of Kellia " *, and that " the 

 fact of the shell being divaricately plicate does not in my 

 opinion entitle it to generic rank, but may be regarded of 

 subgeneric importance." I have again critically examined 

 this species, with the result that I am able to confirm the 

 above observations, perhaps modifying the last statement 

 respecting the relative value of sculpture in separating genera 

 or subgenera. I am now inclined, in this instance, not to admit 

 that it is even of subgeneric importance. 



The dentition of this species is accurately defined by Hinds, 

 H. & A. Adams, and Kobelt ; but Chenu, in his ' Manual/ 

 has described the hinge of Mylitta^ being under the impression 

 that it was synonymous with PytMna. Hinds states that the 

 pallial line is without any sinus ; and on examining three 

 specimens in the British Museum I find this to be correct, 

 for the regular uninterrupted impression is clearly traceable 

 from scar to scar. On the contrary, the existence of " a slight 

 triangular sinus " is mentioned by H. & A. Adams and 

 Kobelt. This error may have arisen through those authors 

 obtaining their information from the description of Mylitta 

 (regarded by them as synonymous with PytMna) given by 



* Stoliczka has restricted Lamarck's comprehensive genus Erycina and 

 made it equivalent to Kellia (Palasout. Indica, vol. iii. p. 2G3j. 



