106 



CARBONIFEROUS L/VMELLIBRANCHIATA. 



described Myalina sublamellosa and M. trigonalis, the latter of which seems to 

 have no affinity to the genus. The genus was redefined by de Koninck in his last 

 great work (' Faune Calc. Carbonif.,' p. 168), and nine species are described : 



Myalina Mosensis, de Kyckholt, one speci- 

 men. 



— lamellosa, de Kon., with which M. 



virgula is included as a synonym. 



— amcena, de Koninck, one specimen. 



— ampliata, de Eyckholt, very rare. 



— depressa, de Koninck, very rare. 



Myalina bursa, de Koninck, one specimen. 



— Goldfussiana, de Koninck, very 



rare. 



— brevialata, de Koninck, one speci- 



men. 



— peralata, de Koninck, three speci- 



mens. 



Of these nine species, seven of which are new, four are founded on single 

 specimens ; of the others it is stated that three are very rare, and that no perfect 

 example of M. Goldfussiana has been seen. I have been able to examine the type 

 specimens of these species now in the Royal Museum at Brussels. It is unfortu- 

 nate that so few specimens of each species have been found ; some of them, too, 

 in a very imperfect condition. I think it very highly probable that any additions 

 to the number of specimens might considerably diminish the number of species. 



The figures of Myalina Goldfussiana and M. lamellosa given in the earlier 

 work of de Koninck differ very much from those in the later publication, and 

 nothing is said in the explanations of the newer plates to indicate that the 

 original figures have been reproduced. M. Goldfussiana, which should be the type 

 of the genus, 4s very unlike all the other forms, being very gibbose and feebly 

 carinated. The only known specimens are the type (?) and a cast, of which 

 M. de Koninck says, " Je considere avec doute .... comme pouvant 

 appartenir a la meme espece." The figure of M. lamellosa, one of the other 

 earlier described species, reminds one very forcibly of the shell figured PI. V, 

 figs. 16 — 19, of Posidoniella elongata, but the view of a fragment with a striated 

 hinge is given along with it ; it is, however, impossible to say whether it belonged 

 to the valve in question, as they are not now in the Natural History Museum at 

 Brussels ; and the figures were not reproduced when the species was re-described. 

 I think it will be found that some of the specimens figured may belong to the 

 genus Posidoniella, which is separated from Myalina by not possessing rostral 

 plates for the anterior adductor muscle, by the twisted anterior border, non- 

 carinate valves, and the absence of striations on the hinge-plate. 



Whidborne, 1 who refers several shells from the Devonian of the south of 

 England to this genus, states, in his definition of Myalina, that it possesses no 

 byssal notch. I think that this statement is not universally correct ; for it is beauti- 

 fully shown in a fragment of M. Redesdalensis from Redesdale, collected by Mr. 

 John Dunn, and figured in PI. Ill, fig. 8. 



' Monogr. Dev. Fauna,' vol. ii, part 1, 1892, p. 45. 



