DESCRIPTION OF GENERA AND SPECIES. 289 



marked by about six narrow, faint, grooved segments which reach half-way across 

 the slopes. Anteriorly, close to the margin and parallel with it, a subangular groove 

 extends from each side of the axis about half-way across the pleural slopes; in front 

 of and outside the lateral extremities of these grooves the surface is abruptly 

 compressed. 



The dimensions of the type specimen are: approximate length 9 mm., width 

 14.5 mm., width of axis anteriorly 4.8 mm., length of axis 7 mm. 



This species is known only from the pygidium, and even that portion is incom- 

 plete. It is referred to the genus Megalaspis by reason of the grooved pleural 

 segments. The segmentation is very faint and would probably be even less distinct 

 or perhaps obsolete entirely were the test of the specimen preserved. 



Illsenus ? bronteoides Weller (plate 26, fig. 10). 



1907. Illanus ? bronteoides Weller, Proc. U. S. Nat. Mus., vol. xxxn, p. 563. 



Pygidium subsemicircular in outline, flattened on top. Axis ill-defined, unseg- 

 mented, occupying a little less than one-third the total width of the pygidium ante- 

 riorly, very slightly elevated in front and merging into the general surface of the 

 pygidium posteriorly. Pleural slopes flattened on each side of the axis, sloping to 

 the margins exteriorly with a slightly concave slope. The surface of each pleural 

 slope, when the test is removed, is marked by about 12 or 13 very narrow and scarcely 

 elevated ribs which are grooved longitudinally and extend from the indefinite axial 

 furrows about to the line where the surface begins its more abrupt slope to the lateral 

 margins. 



The dimensions of the type specimen are: length 8.5 mm., width 14.8 mm., 

 width of axis anteriorly 4.5 mm. 



This species is represented by a single specimen in the collection, a nearly com- 

 plete pygidium. It is a peculiar form having the general contour of an Ulanus. 

 but with the pleural slopes faintly segmented, suggesting the genus Bronleus. These 

 segments are very faint, however, and would possibly not be visible at all were the 

 specimen completely covered with the test. 



Proetus ? sp. undt. (plate 26, fig. n). 



A nearly complete pygidium is referred with some hesitation to the genus 

 Proetus. It is semielliptical in outline, 6. 5 mm. long, and 8 mm. wide. The surface 

 is regularly convex with a concave marginal border, the axis being but slightly ele- 

 vated above the pleural slopes. The axis is divided into about twelve segments and 

 terminates in a bluntly rounded point just within the marginal border. The pleural 

 slopes are marked off by about nine segments somewhat fainter than those of the 

 axis, and reach to the marginal border. In some respects this pygidium suggests 

 some of the asaphids, but without additional material its true relationships can not 

 be certainly established. 



Calymene ? sp. undt. 



A very incomplete pygidium of a trilobite seems to represent a species of Caly- 

 mene, although it is too imperfect to allow even the generic identification to be made 

 with certainty. 

 Pterygometopus ? sp. undt. (plate 26, fig. 12). 



A single imperfect pygidium seems to be referable to this genus. The specimen 

 has a well-defined axis with 1 2 annulations, the pleural slopes being divided into 9 

 segments without longitudinal grooves. 



