OLENELLUS AND OTHER GENERA OF MESONACID^ 333 



OLENELLUS LOGANI, new species 



Plate 41, Figs. 5, 6 



Cephalon transversely semicircular in outline with the marginal 

 border at the genal angles prolonged into slender spines ; strongly 

 convex with the eye lobes and front lobe of the glabella rising 

 abruptly from the cheeks and frontal marginal border ; marginal 

 border very distinctly rounded, strong, and arching up slightly in 

 front of the glabella from the plane of the lower edge of the ceph- 

 alon ; at the genal angles it merges into the genal spine and the nar- 

 row, rounded posterior marginal border of the cephalon ; the latter 

 border is crossed obliquely by a low, slender ridge that is extended 

 beyond the border as a short intergenal spine. 



Glabella with a convex, expanded anterior lobe that rises abruptly 

 from just within the front marginal border; in a small specimen 

 4.5 mm. in length there is a narrow space between the border and 

 the glabella ; the glabella is divided into four lobes and the occipital 

 ring by four pairs of furrows that extend obliquely inward and back- 

 ward from the dorsal furrow on each side to the median line, where 

 they unite, except in the case of the anterior pair which fade out 

 just before reaching the median line ; the second pair of furrows 

 curve backward at their outer end so as to arch nearly around the 

 ends of the third glabellar lobe ; the anterior lobe is as long as the 

 three narrow lobes combined and a little wider than long; it is 

 connected at its postero-lateral margin, on each side, with the pal- 

 pebral lobes by strong, rounded ridges that are a little depressed at 

 the dorsal furrow ; a faint furrow extends inward on each side a 

 short distance from the point where the anterior margin of the 

 palpebral ridges joins the anterior glabellar lobe ; this pair of fur- 

 rows indicates that the lobe is formed of two segments of the original 

 primitive cephalon.' The palpebral segment is beautifully shown 

 by the young of Elliptocephala asophoides [pi. 25, figs. 9 and 10]. 

 The second glabellar lobe is narrow and arched slightly backward 

 at each end so as to nearly enclose the ends of the third lobe, which 

 is thus shortened as compared with the second and fourth lobes ; 

 the third lobe is cut oiT by the arching of the second, but the fourth 

 lobe extends out to the dorsal furrow where, with a very slight in- 

 terruption, it crosses the line of the dorsal furrow and merges into 

 the space within the palpebral lobe ; the third and fourth lobes are 



* This anterior pair of furrows is shown for Paradoxides by Barrande's 

 illustrations of P. spinosus [Barrande, 1852, pi. 12, figs. 2, 3, and 6; pi. 13, 

 fig. i] and P. pusillus [Barrande, 1872, pi. g, fig. 23]. 



