62 Zoological Society. 



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-jjiece complete. 



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

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

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

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

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

 over of the dorsal margin. 



In Myadora, which being a thicker shell requires a hinge of more 

 solid structure, the peculiarities above noted in Anatina and Pandora, 

 the clavicle of the former, the folded margin of the latter, are united 

 in the following modified condition. The dorsal margin of the right 

 valve of Myadora becomes consolidated into a tootli-like ledge or 

 projection, diverging from, on each side, the umbo, fitting into grooved 

 projections of similar construction in the left valve ; and by the di- 

 verging of these tooth-like projections a compact triangular cavity 

 is obtained for the insertion of the ligament, which in some species 

 is walled in, as it were, internally, not laterally as in Anatina, by a 

 moveable testaceous clavicle forming an angle with the diverging 

 ledges. 



The clavicles of Anatina and Myadora, it may be observed, are 

 very diflPerently situated with respect to the ligament, the one being 

 a side appendage, extending across the dorsal axis of the shell ; the 

 other an internal appendage, parallel as it were to the dorsal axis. 



Of the following ten species, which I propose to refer to this genus, 

 the grand type, Myadora striata, is an inhabitant of Port Nicholson, 

 New Zealand, and the remainder are for the most part collected by 

 Mr. Cuming in the Philippine Islands. 



1. Myadora crassa. Anatina crassa, Stutchbury, Zool. Journ. 

 vol. v. p. 100 ; Tab. Supp. xliii. f. 5 and 6. 



Conch. Iconica, Myadora, pi. 1. f. 1. 



Hab. ? 



This short rounded species is the only one at present known in 

 which the right valve is concave. 



2. Myadora trigona. Myad. testd trigond, valde plano-depressd, 

 usque marginem concentride striatd, striis prominentibus , quasi 

 carinulatis, prope marginem anticam undatis ; umbo7iibus acutis- 

 sime mucronato-elevatis . 



Conch. Iconica, Myadora, pi. 1. f. *2. 

 Hab. Catanauan, province of Tayabas, island of Luzon. 

 Four odd valves only of this interesting little species were collected 

 by Mr. Cuming at the above-mentioned locality. 



3. Myadora plana. Myad. testd trigono-oblongd, antici subtrun- 

 catd, planissimd, concentrice striata, striis subdistantibus, valvce 

 sinistra prominentioribus . 



Conch. Iconica, Myadora, pi. 1. f. 3. a and b. 



