246 Annals of the Carnegie Museum. 



The course of the furrows, from the posterior margin, is first diag- 

 onally inward, while crossing the neck ring, which is not otherwise 

 denned, and then straight forward, parallel to the line of the axis. 

 Just before they fade out at the summit of the cephalon they turn ab- 

 ruptly outward. In favorable light three pits may be seen at the 

 bottom of each furrow. 



The cephalon is covered with fine punctae, those on the median lobe 

 being much larger and more numerous than those scattered over the 

 remainder of the surface. The eyes are large, rather prominent, but 

 not pedunculated. 



In ten out of twelve whole individuals the thorax has eight segments. 

 The other two have nine. The segments are narrow, run nearly 

 straight across the body, and turn downward and backward at the 

 sides. Axis about one fifth the width of the dorsal surface, and mod- 

 erately convex, while the pleura are nearly flat. The first four seg- 

 ments are thickly marked with fine punctse arranged in almost straight 

 lines across the thorax, four or five rows to the segment. On the re- 

 maining segments there are very few punctse. 



Pygidium short and wide, somewhat square in front, rounded pos- 

 teriorly. Axis elevated, convex, about half as long as the pygidium. 

 It is isolated by deep furrows at the sides and a slight furrow behind. 

 On the cast the posterior end of the axial lobe is abruptly divided, and 

 back of the axis is a shallow groove which extends nearly to the pos- 

 terior margin. Some of the specimens show three, others four, rings 

 on the axial lobe. The surface is minutely punctate. 



The species approaches Thaleops ovata in having its axial lobe 

 sharply defined on the pygidium and thorax, and in the narrow, 

 strongly outlined glabella. The genal angles also show a tendency 

 toward the formation of spines. On the other hand its close relation- 

 ship to Illcenus conradi connects it with Illcenus rather than Thaleops. 



It is remarkable that in so specialized a group as the Illcenidce there 

 should occur such a primitive character as variation in the number of 

 the thoracic segments. This character has been observed in other spe- 

 cies of the group, notably in Bumastus trentonensis, which may have 

 eight, nine, or ten segments. Clarke, in commenting on Bumastus 

 trentonensis, observes that " Such variations in the degree of segmenta- 

 tion are not, indeed, usual in the mature condition of a species ; they 

 are, however, altogether in harmony with the laws of morphogeny, 

 and deviations from the normal Trenton type with ten segments are 



