91 



dicates their reepective terrestrial and aąUatic habits, was correot, 



and gavę due credit to ita proposer." 



" Monograph of the genus Myadora, a small group of Acephaloue 

 MoUueks of the family Myaria," by Loveli Reeve, Esą. 



Genus Myadora, Gray. 



Testą trigono-ovata, inaguivalvis, valvd sinistrd plūs mtnusve con- 



cavd, dextrd pland, rarb concaviusculd ; incEcuilateralis, latere 



postico rotundato, antico leviter flemioso, coarctato, inferne ple- 



rumque truncato, dejn-essione plano-concavd sub umbones. Cardo : 



dentibus in valvd dextrd duobus lateralibus, elongatis, rtidibus, ab 



umbone divergentibiis, quorumposticus planus, subobsoletus ; in valvd 



sinistrd projecturis sulcatis duabus lateralibus, dentes recipientibus. 



Ligamentum internum infoved trigond centrali inter dentes inser- 



tum, appendice testaced concavd stepe interne protectum. Valvce 



intus margaritacete, pallii impressione musculari antice sinuatd. 



The genus Myadora, introduced by Mr. Gray in his account of the 



• Shells of Molluscous Animals/ in the ' Synopsis of the Contents of 



the British Museum,' is one that cannot fail to be appreciated ; 



nothing indeed can more fuUy demonstrate the necessity for a new 



generic allotment of certain species, than the cireumstance of their 



having been transported at different tlmes from one genus to another 



by the šame author*. 



The Myadora partake of the characters of Anatina and Pandora, 

 and as they have been refeired at times to both of those genera, it 

 is important to describe with some minuteness the difFerences which 

 entitle them to generic distinction. In Anatina the hinge is com- 

 posed of two hollow spoon-shaped processes, containing the liga- 

 ment, protected in some species by a moveable testaceous clavicle, 

 which crosses the dorsal axis of the shell on the posterior side, as in 

 the Anatina truncata, for example, a species now commonly obtained 

 with the accessory hinge-piece complete. 



In Pandora, \vhich is too flat and compressed a shell to admit any 

 structure likę the spoon-shaped processes of Anatina, the ligament 

 is lodged in a cicatrix, protected on the posterior side by a single 

 centrai oblong tooth in the right valve only ; the clavicle is dispensed 

 with, but the loss is in a degree supplied l)y a thickening and folding 

 over of the dorsal margin. 



In Myadora, which being a thioker ehell requires a hinge of more 



• " In an Appendix to a Catalogue of Shells collected in the Australian 

 and Polynesian group, by Mr. S. Stutchbuvy," says Sowerby, in his account 

 of the genus Pandora, ' Species Conchylioruni,' Part 1, " I have described, 

 under the name oi Pandora brevis, a shell {Myadora brevis, nobis) \vhich I am 

 no\v convinced is rathev an Anatina, inasmuch as its flat valve is destitute 

 of the bhint tooth which characterizes Ihe Pandora ; it differs also from 

 them in having a sinus in the muscular impression of the mantle, and in 

 being possessed of a small testaceous appendage attached to the ligament." 

 Tliis shell it \viU be seen bowever bas not the spoon-shaped processes of 

 Anatina. 



