OF THE SPECIES. 105 



B. 



The body axis cotmstinr/ of nine rings. 

 Genus 18. — Dysplanus. 



Cephalic shield highly arched, large, semilunar, the posterior angles elongated into 

 pointed processes, the glabella not more strongly arched, and no posterior j)roniinent 

 margin of articulation. 



The facial suture describes in front a semicircle, bends towards the eyes, and extends 

 with a gentle curve from the latter to the posterior margin ; between its extremity and the 

 glabella there is at each side a furrow. 



Eyes small, slightly convex, scarcely rising above the level surface of the head, placed 

 still further towards the exterior part than in Ulanns, lunate, transparently reticulated. 



Body axis rather convex, but the rings are short ; the lateral lobes rather broader 

 than the axis, strongly bent downwards, without diagonal furrows. 



Caudal shield broad, semicircular, slightly arched, with a short, slightly indicated conical 

 ixis, without rings or lateral furrows. 



The only known species is : 



D. centrofiis ; Asaph {Illesnus) centrot. Dalm. Pahead. 51. 11, Tab. V, Fig. 1, a. c. 

 BoECK, Gaea Norm. I, No. 35. Emmr. Dissert. 34, 18. Isotcles centr. Milne 

 Edw. Crust, 301. 7. 



LocaUti/. — The transition lime of Eastgothland, near Husbyfjöl, but of rare occurrence ; 

 found also at Christiania. 



C. 



The axis of the body consisting of eight equal rings. 



Genus 19. — Asaphus, Brong. (Asaphus et Nileus, Dalm. ; Isoteles, Dekay ; 

 Hejucrypturus, Green.) 



This genus embraces a widely extended group, if we define it according to the number 

 of the rings of the body ; but in addition to these it only exhibits one other generic character, 

 derived from the course of the entire facial suture, on the upper side of the cephalic shield. 

 Intersecting the margin at the posterior part, in the centre of the lateral lobes, this suture 

 turns with the usual S-shaped curve towards the eye, forms over it the covering plate, and 

 thence extends, describing an arch to the centre of the anterior margin. The two angles 

 pass into one another, describing a semicircle, if the anterior margin is obtuse, and they 

 form an angle with one another if the latter is pointed. The eyes themselves are large, 

 high, and exceedingly prominent, although not quite so elevated as in Thacops ; the thick 

 horny membrane is smooth, but the lenses are not unfrequently seen through it. 



The axis of the body is of equal breadth, rather broader perhaps towards the centre, 

 and usually distinctly separated from the lateral lobes ; the oblique transverse furrows are 

 then visible likewise. 



The caudal shield resembles the cephalic, either wholly or very nearly in point of 



14 



