Dr. J. E. Gray on the Names of the Genus Mystoinys. 425 



27. Primitia muta, no v. 

 Cytheropsis concinna?, ibid. p. 254, pi. 9. fig. .'5. 

 Oblong-ovate, nearly Leperditia-shajped ; back straight, ends 

 rounded but unequal; ventral edge convex; surface smooth. 

 Though resembling P. concinna at first sight, it is less cylin- 

 drical, broader at the obliquely rounded end, and its ventral 

 dge is more symmetrically curved : it is near to P. rugulifera in 

 shape. From the Upper Silurian Limestone of Beechey Island, 

 with P. rugulifera, P. sigillata, Beyrichia clathrata, B. plagosa, 

 and Leperditia gibbera. 



EXPLANATION OF PLATE XIII. 

 [The figures are magnified about 20 diameters.] 



Fig. I. Primitia cristata, J. & II.: a, carapace, view of right valve; 



b, posterior view ; c, dorsal view. 



Fig. 2. P. umbilicata, J. & II. : a, left side of carapace; b, dorsal view; 



c, ventral view; d. inside of valve (filled with matrix). 



Fig. 3. P. tersa, J. & II. : a, carapace, side view; b, dorsal view; c, ven- 

 tral view. 



Fig. 4. P. trigonalis, J. & II. : a, carapace, view of left valve; b, dorsal 

 view. 



Fig. 5. P. renulina, J. & II. : a, carapace, side view; b, dorsal view. 



Fig. 6. P. variolata, J. & II.: a, left valve; b, its edge-view; c, right 

 valve of var. paucipunctata ; d, its edge view. 



Fig. 7- P- matutina, J. & II. : a, right valve; b, its edge view. 



Fig. 8. P. Roemeriana, J. & II. : a, carapace, side view (left valve); b, pro- 

 file. 



Fig. 9. P. Beyrichia na, J. & PL, right valve. 



Fig. 10. P. semicircularis, J. & H. : a, left valve; b, its end view ; c, ven- 

 tral edge. 



Fig. 11. P. pusilla, J. & II. : a, right valve; 6, its edge view. 



Fig. 12. P. obsoleta, J. & II.: «, right valve; b, its end view; c, edge 

 view (ventral). 



Fig. 13. P. ovata, J. & II. : a, right valve; b, its end view; c, edge view 

 (ventral). 



Fi</. 14. P. oblonga, J. & H. : «, right (?) valve; b, its end view ; c, edge 

 view (ventral). 



XLVIII. — On the Names of the Genus Mystomys. (In a Letter 

 to Professor Allman.) By Dr. J. E. Gray, F.U.S., V.P.Z.S., 

 F.L.S. &c. 



British Museum, Nov. 15, 18(i5. 

 Dear Professor Allman, 



As I have been informed that, in your paper on the animal 

 that DuChaillu noticed as Cynogale velox, you persist in retain- 

 ing the generic name of Potamogale, I venture to send you the 

 following observations, in the hope that I may induce you to re- 

 consider the question, and avoid adding another to the several 

 useless names which the animal has already received. 



