OLENELLUS AXD OTHER GENERA OF MESOXACID/E 29I 



illustrated by figs. 5, 6, and 7, pi. 40. By the aid of these specimens 

 and the casts and Dr. Moberg's ver\- detailed descriptions the fol- 

 lowing brief description is drawn up : 



Cephalon semicircular, strongly convex. Width a little less than 

 one-half the length ; marginal rim liroad, flattened and separated 

 from the cheeks by a shallow furrow ; it widens from the front 

 toward the genal angles and is probabh- produced into strong, flat- 

 tened genal spines; posterior marginal' rim about as wide as the 

 rim in front of the glabella ; it is faintly defined by a narrow, shal- 

 low furrovv'. Glabella widening a little from the occipital ring to 

 the anterior end of the eye lobes where it expands into the large 

 anterior lobe ; the latter rises abruptly from just within the mar- 

 ginal rim and curves over to the level plane along the median line 

 of the glabella ; the glabella is marked by three pairs of lateral fur- 

 rows joined across the glabella by a fainter furrow. The size and 

 position of the furrows and the glabellar lobes are shown by figs. 

 4 and 5. The occipital ring is subequal in width to the fourth lobe 

 of the glabella ; it has a small, pointed median tubercle at the pos- 

 terior margin. The palpebral lobes start from the postero-lateral 

 portion of the large anterior glabellar lobes, and arch backward to 

 a point opposite the front of the occipital ring ; they are eleyated 

 nearly to the plane of the median line of the glabella and leave a 

 depressed space between them and the dorsal furrow beside the 

 glabella ; sometimes a small intergenal spine is indicated at the end 

 of a narrow elevated line extending from about the end of the 

 occipital furrow. Dr. Aloberg states that approximately parallel 

 to this line is another fainter line, which extends from the posterior 

 part of the eye, that he is inclined to consider an obliterated facial 

 suture. He also noted traces of a similar line in front of the eye. 

 The cheeks rise rapidly from the furrow within the marginal rim 

 to the base of the eye. 



The hypostoma is shown by fig. 6. No traces of spines or tu- 

 bercles are shown on any specimens I have seen of the back and 

 lateral margins, and Dr. Moberg did not note any marginal spines. 



The median lobe of the thoracic segments is distinctly separated 

 from the pleural lobes ; a strong median spine with an elongated base 

 occurs on many of the fragments of the median lobe ; on other 

 specimens a small tubercle is all that is seen, Dr. Moberg draws 

 the conclusion from this that the anterior segments had small, weak 

 spines, and that the spines increased in strength on the middle seg- 

 ments ; the pleural lobe of the middle segments extend out directly 



