90 CARBONIFEROUS LAMELLIBRANCHIATA. 



Fig. 19, PI. V, is the cast of a perfect example, and shows the two valves in 

 apposition. Fig. 18, PI. V, is the cast of a left valve, and this example shows the 

 character of the anterior adductor. Although the casts seem to be in a good state 

 of preservation, and the posterior adductor scar is just visible, I can see no 

 indications of pallial line. 



Like P. pijriformis, the shell, as a single valve, has a marked resemblance to 

 the Gasteropod form Capulus, especially if the shell be held with the umbo 

 directly vertical. This resemblance is due to the acute angle at which the anterior 

 surface and hinge-line meet, and their short extent. 



A fourth specimen has been obtained by Mr. J. Dunn from the Coombes 

 Limestone of Redesdale, Northumberland, PI. V, fig. 17. This is somewhat 

 smaller than the Yorkshire specimens, and has the two valves crushed together 

 to a slight extent in front, and therefore does not give a typical view of the 

 anterior surface. This specimen fortunately shows in the right valve the pallial 

 line and posterior adductor muscle-scar. The position of this scar at once 

 separates the genus from Avicula, which has its scar subcentral. 



A fifth specimen is numbered 67 g in the collection of Mr. Gr. H. Morton, of 

 Liverpool, who has kindly permitted me to figure it. This is a left valve, and has 

 the test preserved in a beautiful condition, PI. V, fig. 15 ; but the locality 

 unfortunately is not recorded. 



I consider it highly probable that the original of Phillips's Modiola elongata 

 belonged to the species under description, although we cannot be certain 

 in the absence of the type. This is stated to have been in the Grilbertson 

 Collection, but no shell now in that collection in the British Museum can be 

 identified with the drawing. The original description is meagre, but suits the 

 shells of the Cambridge Collection exactly, being as follows : — " Elongate, arcuate, 

 margins subparallel, valves gibbous, subcarinatecl." I have therefore retained the 

 specific name elongata. An additional reason for the probability of the identity 

 of these shells with that of Phillips's type is that they are from the same district, 

 Bolland. 



One of the figures of Myalina lamellosa given by de Koninck (op. cit.) is so 

 remarkably like the shell under description, and so different from the other 

 specimens subsequently figured by him, that I have placed it with a ? as a 

 synonym. True, the figure is stated to be 6 c, but it is not now certain that 

 fig. 6 a, which shows the striated hinge-plate of the then new genus, was a portion 

 of the same specimen, fig. 6 a being represented as a mere fragment. It is a pity 

 that the original figure was not reproduced in de Koninck's great work on the 

 Carboniferous Lamellibranchiata in 1885. 



