76 SYSTEMATIC ARRANGEMENT 



extended, but assumes a more vertical position at the sides, and terminates at each side in 

 a point, which is produced posteriorly for three fourths the length of the animal. Its border 

 is rather thickened, and forms (both on its upper and lower reduplication) an elevated 

 bordering line. From this horseshoe-formed extension of the margin, the head rises ante- 

 riorly and laterally with a somewhat steep elevation, and in the middle of the elevated part 

 it has an oval protuberance in the manner of a forehead, which is surrounded by an im- 

 pressed furrow, and which does not descend to the expanded margin. It forms a keel (a 

 very slight one, Akc.) at its highest part, and exhibits a slight fold in front of the furrow on 

 the summit. A small semicircular eye-tubercle is situated on each of the large cheeks, 

 almost at the anterior extremity of this fold, and close to it. Even with the naked eye one 

 can distinguish a somewhat larger round protuberance at the centre of this eye-tubercle, and 

 two oval ones of the same size on both sides.* Behind them may be discovered, with the 

 assistance of a microscope, other small tubercles in regular rows. 



"The head terminates posteriorly in a small protuberant half-ring, to which the joints 

 of the central body are united. The protuberance of the forehead and the summit of the 

 cheeks above the eyes, are smooth ; and it is only upon the furrow of the former that a few 

 small granulations are perceptible. The rest of the surface of the head is thickly granu- 

 lated, so that the boundary towards the smooth forehead is distinctly marked, f 



" The expansion of the margin is prettily ornamented by a row of larger granulations 

 on the surface, both of its upper and lower plate, and as well at the external as internal 

 margin (i. e. in the cast ; in the true shell there are corresponding indentations, and no 

 granulations, Auc) 



" From the head to the side of the tail, twenty-eight segments may be counted, 

 becoming gradually and uniformly shorter towards the posterior part. Whether there is 

 also a small simple caudal shield without ribs, cannot be determined from the specimens 

 before us. The high convex spine (the axis) occupies a third part of the whole breadth, 

 and its segments are ring-shaped; the ribs, however (lateral lobes), have only a fiat 

 longitudinal furrow, are closely united, and form a flat expansion at each side. Their short 

 ends are obtusely pointed and bent downwards at an angle, so that the body exhibits a 

 narrow border. The anterior ribs (lateral lobes) increase gradually in length^ as far as the 

 seventh or eighth, and the rest become gradually narrowed again behind them. The spine 

 is granulated, but the sides are quite smooth." 



The specimen in my possession has no trace of body rings ; but I suppose from the analogy of 

 the cephalic shield that the rings of the axis were also without granules, and merely ornamented with 

 punctiu'es, Auc. 



* These parts are absent in the specimen which I possess ; judging from the figure, I should 

 suppose that only the two oval spots are real eyes, and that the warts are little prominences on the 

 shell. This genus would otherwise be characterized by four eyes, two on either side. 



t Goldfuss is here describing an impression without the shell, in fact, a cast in which all the 

 indentations of the real shell appear as protuberances and granulations. In the same way Count 

 Münster describes young individuals for his Trinuclens. 



X The breadth is from left to right. 



