ILLJENUS. 



205 



and gently convex and obtusely margined, while that of //. instants is pyramidal and the 

 margin recurved. The latter species is abundant in North America, as described by 

 Hall ; and I do not know^ if the huge imperator, lately described as a distinct species 

 by that author (Reports, Dec, 1864), be different or not. It may be, for aught in the 

 description, a giant form of this large species. 



It will be perceived that these three species diflFer in form and sculpture. //. 

 Barriensis is depressed in the front view (fig. 53), and has coarse squamate striae in 

 front. //. insignis (fig. 52), more elevated, and with a deep pit where the obscure 

 glabellar furrows end, has very fine ornamental striae. //. carinatm (fig. 53), the most 

 gibbous of all in a front view, has the axal pits like //. insignis, and the coarse striae, 

 less universal than in //. Barriensis. 



British Upper Silurian Ill^ni of the Section Bumastus. 

 Tig. 51. Tig. 52. Fig. 53. 



H. carinatus, Salter. 11. insignis, Hall. II. Barriensis, Murch. 



Wenlock Limestone, Malvern; The common Dudley fossil. Very common in the Woolhope Beds 



a rare species. usually called I. Barriensis. and Wenlock Shale. 



//. Barriensis is broad-oval, with blunt extremities and arched sides. The head mea- 

 sures very nearly an inch and a half long, and is therefore rather less than a third of the 

 whole length. The tail is exactly as long as the head, — the body (of 10 arched rings) 

 occupying one inch ten lines, and being therefore longer than either. The trilobation is 

 extremely faint, and the breadth of the axis as great proportionally as in Homalonotus. 

 The fulcra] point nearly coincides with the faint axal line (it can scarcely be called a 

 furrow). However, the axal furrows are strongly marked out for a short distance in 

 the head ; and we may now describe that portion. 



Head forming nearly a quarter of a sphere, and not more pointed in the young 

 than in the old state, the front being obtuse in all ages, and more flattened anteriorly and 

 on the sides than a true semicircle. It is depressed, the vertical height being only half the 

 width ; and the convexity being spread over the whole surface, the view of the front edge 

 (woodcut 53) presents a semicircular outline instead of a subpyramidal one. The edge is 

 blunt and convex all round, not at all recurved. The axal furrows converge very strongly 



