152 ON PERMIAN ENTOMOHTKACA FROM 



The chief variation of form shown by this species is in the 

 dorsal margin, which is more prominent in some individuals than 

 in the majority. Fig. 2, pi. X., illustrates this variety. 



C. Jonesiana resembles in many respects the Cythere Geinitzi- 

 ana* of Jones, which appears to be a closely related form. The 

 dorsal margin of the latter, however, is more flatly convex, its 

 posterior extremity is more acutely pointed, and medianly placed, 

 and the sinus of the ventral margin is deeper than the same fea- 

 ture in C. Jonesiana. The lateral contour is peculiar also, being 

 ovate, while that of C. Geinitziana is a flattened oval, with rather 

 acute extremities. In these particulars it difl'ers from the pre- 

 sent species; and I allow them specific value. 



Most of the specimens of this species which have occurred at 

 Tunstall Hill are coated with a thin deposit of calcareous mat- 

 ter; and it is not until this is removed that the hingement of the 

 carapace can be detected. 



It is not rare in the shell-limestone of Tunstall ; it also occurs 

 at Hampole, Yorkshire. In Germany it is found in the Unter 

 Zechstein of Bleichenbach and Selters. 



C. Jonesiana is named after my friend Mr. T. Rupert Jones, 

 to whom I am indebted for several courteous communications on 

 Permian Entomostraca. 



NOTE BY MR. T. R. JONES ON CYTHERE JONESIANA, KIRKBY. 



C. Jonesiana (Kirkby) and C. Geinitziana (Jones) are, with- 

 out doubt, closely allied to each other, and to the forms termed 

 by Reuss Bairdia frumentmn and B. (jraciUs. Indeed, thei*e are 

 very many CytJw^es, both recent and fossil, having modifications 

 of this form of carapace, such as C. /lauida, C. angn.sta., &c. ; and 

 it is often hazardous to distribute the fossil valves into specific 

 groups, there being little except slight differences of marginal 

 outline and lateral contour to be taken as criterions. Still less 

 can we feel satisfied either in distinctions or synonyms, when we 

 have only plain lithographs (in the case of many of the foreign 

 Entomostraca) to judge by. For the present, we had better 

 keep provisionally distinct the best marked forms, until we can 



* Jones, ill " Kind's Moii. Porin. Foss.,'" p. 02, j)!. XVIH., lljr. 4, a, h, c. 



