318 Lower-Carhoniferous Entomostraca. By T. R. Jonfts 



its being placed generically with any of them. 



With my new views of its alliance, it is now described as 

 having a moderately convex, bean-shaped carapace, with sub- 

 oblong, equal valves, broader (higher) at one end (anterior) than 

 at the other. The largest carapace is 1*5 millimetre long, and 

 the width (height) of the valves is more than half the length by 

 A of the length. Both ends are rounded, but the large curve of 

 the anterior margin is slightly flattened above in front of the 

 hinge-line ; and the hinder curve is slightly compressed at its 

 lower half. Dorsal border straight along the hinge-line, which 

 extends from a fifth of the length of the valve from the posterior, 

 to nearly a third of the valve's length from the front. The sur- 

 face is smooth to the eye, but, when magnified, shews a radiating 

 reticulation, which varies in intensity in different individuals ; it 

 is also impressed with a shallow furrow in the middle third of the 

 dorsal region, reaching to the centre of the valve ; and it bears a 

 small submedial tubercle in front of the sulcus, accompanied by 

 some small irregular depressions of the surface ; seen edgeways 

 the carapace has a long, narrow, oval shape, with sharp ends ; 

 end-wise it is subovate. The radiate ornament on the valves 

 from Northumberland reminds us of a similar marking sometimes 

 visible on the outside of Leperditia ( L. ardicaj, and always on the 

 inside or cast. But the broad, definite, central muscle-spot and 

 the escutcheoned eye-spot of Leperditia are both wanting ; and the 

 dorsal furrow, though present in Primiiia, is not a Leperditian 

 feature. 



A coarse radiate reticulation is present in the Silurian Beyrichia 

 clathrata, Jones, from Beechey Island, but the true Beyrichian 

 furrows and lobe distinguish this form. 



In some respects Carhonia '^ seems to be a near ally of the form 

 under notice ; but it is not dorso-sulcate. Some of the Carbonice 

 have the submedial tubercle, and an external sculpturing ; but 

 the latter appears as longitudinal striae f or simple reticulation J. 



In Carlonia the smallest end is taken for the anterior, and the 

 right valve is larger than the left, the dorsal line convex and the 

 ventral nearly straight. In the specimens before us the largest 



* "Geol. Mag." vol. vii., 1870, p. 218, pi. 9, figs. 4—10 ; and "Ann. Mag. 

 N.H." ser. 5, vol. vi., 1879, p. 30, pis. 2 and 3. 



t "Geol. Mag." loc. cit. figs. 4, 8, 10. 



t "Ann. M. N. H." loc. cit. pi. 2, figs. 9, 10, and pi. 3, fig. 8. 



