420 Prof. T. R. Jones and Dr. H. B. Holl on 



some of the characteristics of the Lower Silurian P. bicomis, 

 but in a much less degree. 



From the Upper Silurian (Scandinavian) Limestone found as 

 drifted blocks in North Germany. We have seen a small speci- 

 men in a limestone of the Wenlock Series from near Malvern. 



13. Primitia nana, nov. 

 Beyrichia strangulata, var. y, ibid. p. 173, pi. 6. fig. 22. 

 Very small, nearly oblong, but proportionally longer than P. 

 strangulata. Edges of sulcus swollen into two minute unequal 

 tubercles. In soft fossiliferous schist (Lower Silurian) at Har- 

 nage, near Shrewsbury, in company with P. simplex and P. bi- 

 comis. It is possibly the young of the latter. 



14. Primitia bicomis, Jones. 



Beyrichia bicornis, ibid. fig. 23. 



Very small, but readily distinguished by its two subcylindrical 



tubercles bordering the sulcus on each valve, and by its crested 



marginal rim. From the Lower Silurian beds at Harnage, near 



Shrewsbury. 



15. Primitia umbilicata, nov. PI. XIII. figs. 2 a, b, c, d. 



Length — o~5-o> height -y%%-^, thickness -rlw inch. 



Carapace convex, rounded-oblong ; dorsal angles sharp ; 

 hinge-line straight, and sunken in an elliptical or acute-ovate 

 depression formed by the convexity of the dorsal borders of the 

 two valves; this flattened area is broadest posteriorly, and ter- 

 minates, near the antero-dorsal angle, by a slight notch. The 

 hinge itself is formed by the meeting of simple edges. The 

 ends of the valves are boldly rounded ; the ventral line is gently 

 convex; surface of the valves convex, rather compressed in 

 front, usually smooth, but sometimes ornamented with minute, 

 close-set, undulating lines. Each valve is marked in the middle 

 with a short longitudinal furrow, more or less pronounced in 

 different individuals, and widened at its centre into a navel-like 

 pit. A well-defined rim extends from one dorsal angle to the 

 other, round the ventral border of each valve, nearly parallel to 

 the edge, from which it is separated by a shallow groove. The 

 edge itself is sculptured with minute transverse pits. 



This is the characteristic Primitia of the Aymestry Limestone 

 of Chances Pitch, near Malvern. 



16. Primitia cristata, nov. PI. XIII. figs. 1 a,b,c. 



Length -to-o-o* height -r?ro-oj thickness -nroif inch. 

 Carapace convex, but most tumid posteriorly ; suborbicular 

 or rounded-oblong, and about one-third longer than high. 



