330 



Explanation of the Plates. 



Platyceras primordialis. 



Pig. 28. A nearly entire individual. The specimen is of the medium size among those in the 

 collection. 



EUOMPHALUS ? VATICINUS. 

 Fig. 29. The upper side of the spire. The specimen is somewhat distorted. 



Theca primordialis. 



Figs. 30 & 31. Figures showing the opposite sides of the shell. 



Serpulites murchisoni. 



Fig. 32. A figure of the natural size of the specimen. 



Ptychaspis granulosa. 



Fig. 33. A figure of a small head, enlarged two diameters, to show the exterior markings. 

 " 34. A cast of a larger individual, natural size. 

 " 35. A profile of the same in outline. 



" 36. The head of a very small individual, enlarged three diameters. The specimen shows a 



broader glabella in front, with distinct eye-lobes on the fixed cheeks. 

 " 37 & 38. Profile and lateral views of a cheek of this species. 

 " 39. A part of a thoracic segment. 



" 40. A large pj r gidium, corresponding with the one referred to this species by Dr. Owen. 

 Specimens of the head of this species, at least once and a half as large as fig. 34, have been seen 

 in the same association. v 



Ptychaspis miniscaensis. 



Fig. 41. The glabella and fixed cheeks of an individual of medium size. 

 n 42. A profile of the same. 



" 43. A much smaller head, given for comparison with Ptychaspis granulosa, f. 34. 

 M 44. A profile of the same. 



" 45. A cheek of this species, the figure of natural size. 

 " 46. A pygidium of the same species. 



M 47. A segment of the body, found in the same association, but probably belonging to 

 Chariocephaltjs. 



Ptychaspis, sp. ? 



Fig. 48. The head of a very small individual of an undetermined species. It may possibly be the 

 young of one of the above species. 



Chariocephalus whitfieldi. 



Fig. 49. The glabella and fixed cheeks, showing a curving frontal limb, and without visible fur- 

 rows in the glabella, which is a cast. The figure of natural size. 



" 50. A specimen preserving the glabella and fixed cheeks, where the frontal limb is nearly 

 straight. There are two pairs of furrows distinctly marked in the glabella. The figure 

 is twice the natural size of the specimen. 



" 51. A profile of the preceding specimen. 



" 52. A movable cheek of this trilobite, natural size. 



" 53. A smaller movable cheek of the same species. 



Agnostus JOSEPIIA. 



F13. 54. The head of this species, showing the short spines at the postero-lateral angles. 

 11 55. The pygidium of the same species. 

 These figures are enlarged three diameters. 



