288 CARBONIFEROUS LAMELLIBRANCHIATA. 



Observations. — This genus was erected by de Koninck, who professed to take 

 the Isocardia unioniformis of Phillips as his type, but the shells which he figured 

 as belonging to this species are quite different, being almost orbicular, as he says, 

 "a pen pres ronde ; " but fortunately Phillips's shell undoubtedly belongs to the 

 genus Edmondia, and therefore may still be considered as the type of this genus. 

 Part of the original generic diagnosis is as follows : " Lunule echancree ; charniere 

 depourvu de dents, remplacees par une lamelle transverse, etroite, profondement 

 situee et en partie recouverte par le crochet et ayant probablement servi a sup- 

 porter un ligament interne d'une form a peu pres analogue." The figures show 

 conclusively that there is no lunule, and no mention is made of this character in 

 the amended diagnosis of 1885 (op. supra cit.), which states that the hinge is 

 " depourvue de dents, munie de grands plaques du cartilage, obliques, placees 

 au-dessous des crochets." 



Fortunately many specimens of different species showing the hinge have 

 been obtained from Tournai, one of which I figure, PI. XXVII, figs. 16 a, b, 

 but none of these show any indications of cartilage-plates ; but there is, however, 

 as is stated in the first description, a curved transverse lamella, situated deeply, 

 and separated from the edge of the shell by a groove parallel to it, which 

 does not extend forward in front of the umbo. Probably, as de Koninck 

 observed, this groove did contain some structure of the nature of an internal 

 ligament. In casts this ridge is represented by a well-marked groove between 

 the umbo and the edge of the valve ; but external to it in the hollow of the umbo 

 is a deep groove, which extends forwards in front of the umbo and also passes 

 backwards, becoming wider and broader, to within a short distance from the 

 postero-superior angle, in which lodged a process of shell ; from the splendid way 

 in which in many specimens this groove is preserved, I should incline to the view 

 that it had originally contained an ossicle and not cartilage. 



Professor King referred a shell to this genus, under the name Edmondia 

 sulcata ('Monog. Permian Fossils,' pp. 163-4, pi. xx, figs. 1 — 4), which has 

 somewhat similar well-marked internal ossicles ; but the arrangement, shape, 

 and the whole structure of this shell and process differ from that which is found 

 in the more ovate smooth-shelled group of Edmondia. That the process was of 

 shelly structure, and not cartilaginous, is evident from the preservation of this 

 portion of the hinge in a specimen of E. Pentonensis. M'Coy placed Edmondia 

 with the Mytilidse ; but King erected a new family, Edmondidse, which he placed 

 immediately after the MytilidsR. The valves are, however, always equal, and there 

 i> ;i well-marked but small external ligament, and no constriction of the valves or 

 other indications of a byssus in Edmondia. 



De Verneuil confounded Edmondia and Allorisma. His specimen on pi. xix, 

 figs. 6 «, b, agrees undoubtedly with the Allorisma of King; but the shell figured 



