SOLENOMYIDiE. 437 



The amount of overlapping, in the series of British specimens which I have 

 been able to examine, is very variable, being absent in some and very marked in 

 others. The absence of gaping behind may be due to the fact that there is a slight 

 amount of dislocation of the valves posteriorly. M'Coy's type has been consider- 

 ably improved upon in the original drawing. The overlapping itself in this 

 specimen is of the slightest amount, and the shell appears to gape only in front ;, 

 and further, Beushausen's figures (pi. xxvi, figs. 1 c, 2 c, 4 c) do not show any 

 overlapping of the valves, and only the smallest degree of inequality in the valve. 



Beushausen admits that living and Palseozoic forms have a certain remote 

 (weitgehende) resemblance in shape, sculpture, position of ligaments, and muscle- 

 scars. But he considers that there is some little difference in the character of 

 the posterior end of the ligament. With regard to the question of the gaping of 

 the shell, he thinks that 8. ])rimxva gapes in front only, and 8. hiarmica at both 

 ends. It seems to me, therefore, that the separation of Janeia and 8oIenomya is 

 based on problematical characters only, while all the important points of resem- 

 blance are considered of no value. I am therefore unable to follow Herr 

 Beushausen, and see no reason for accepting his emended genus Janeia. 



Beushausen thinks Clinopistha (Meek and Worthen) to be unnecessary. 

 But here again I am unable to agree with him. The shells referred to Glinojjistha 

 by Meek and Worthen, and by de Koninck, differ so markedly in shape, sculpture, 

 and general character from Solenomya that the retention of the genus is very 

 useful. Beushausen says that intermediate forms exist, as shown by his speci- 

 mens. This is probable, but none of the specimens figured by him have the 

 contour of the type of Clinopistha ; the only one approaching it, ./. truncata (pi. 

 xxvi, figs. 4a — c), being too transverse. Clinopistha certainly was closed all 

 round. 



Beushausen seeks to strengthen his case by stating that some specimens of 

 AllorlsDia gape and others do not. I do not think that any species of Allovisma 

 gape, and that the appearance of gaping in some specimens is merely due to the 

 fact that the shell was filled with mud, and was fossilised with the valves somewhat 

 open, though still connected along the hinge-line; a condition which must have 

 happened when dead shells were filled. 



I recognise three species of 8olenomya. in British Carboniferous rocks ; two of 

 which are also found in the limestone of Belgium, and one I am unable to distin- 

 guish from a North-American form, 8. radiata, Meek and Worthen. Two Belgian 

 forms {8. saginata, 8. parallela) I am not able to find in England. 



Edmondia arcuata, Phillips, sp., was referred to 8olenomya by de Ryckholt {op. 

 cit.). One can well understand that he did so. As I have pointed out above, p. 

 311, this species has the anterior adductor muscle-scar in a different position from 

 the rest of the species of the genus, and if the long end of this shell was supposed 



