Zoological Society, 61 



a distinct cavity, by introducing from the outside a small blunted 

 wire, with which I gently pressed the sides ; it seemed however not 

 so extensive anteriorly, posteriorly, and at the angles, as I should 

 have supposed from the form of the more solid supports outside. 



" The rest of the anatomy of this animal I must leave until 1 can 

 procure more specimens and have more leisure. 



" When I first got the Megascolex I was sure I had obtained an 

 animal which would break down the old division of A branches seti- 

 geres and A. sans soies, for the bristles are so minute that I did not 

 in the first instance perceive them. As to its being a true Lumhricus 

 there could be no doubt. I was much gratified when I discovered 

 that the separation of the tribes, founded on a character which in- 

 dicates their respective terrestrial and aquatic habits, was correct, 

 and gave due credit to its proposer." 



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

 MoUusks of the family Myaria," by Lovell Reeve, Esq. 



Genus Myadora, Gray. 



Testa trigono-ovata, incBquivalvis, valvd sinistrd plus minusve con- 



cava, dextrd pland, raro concaviusculd ; incequilateralis, latere 



postico rotundato, antico leviter jlexuoso, coarctato, inferne pie- 



rumque truncato, depressione plano-concavd sub umbones. Cardo : 



dentibus in valvd dextrd duobus lateralibus, elongatis, rudibus, ah 



umbone divergentibus, quorum posticus planus, subobsoletus ; in valvd 



sinistrd projecturis sulcatis duabus lateralibus, dentes recipientibus, 



Ligamentum internum infoved trigond centrali inter dentes inser- 



tum, appendice testaced concavd scepe interne protectum. Valva 



intus margaritacece, 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 fully demonstrate the necessity for a new 



generic allotment of certain species, than the circumstance of their 



having been transported at different times from one genus to another 



by the same author*. 



The MyadorcR partake of the characters of Anatina and Pandora, 

 and as they have been referred 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- 



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

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

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

 under the name o^ Pandora brevis, a shell {Myadora brevis, nobis) which I am 

 now convinced is rather an Anatina, inasmuch as its flat valve is destitute 

 of the blunt tooth which characterizes the 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." 

 This shell it will be seen however has not the spoon-shaped processes of 

 Anatina. 



