May, 191 /J Silurian Fossils from Ohio 253 



these casts, the narrow median lobe of the glabella, huniped posteriorly 

 and narrowing sHghtly anteriorly, closely resembles that of the Mills 

 quarry specimen, here figured and described, thus ])rcsenting the most 

 characteristic feature displa\-ed b\' the latter. The compound anterior 

 lateral lobes and the anterior outlines of the third lateral lobse also are 

 similar but it is evident that the posterior part of the third lateral lobes 

 was cut away in cleaning the original specimen, thus producing a 

 straightness of outline which is entirely misleading. Moreover, the 

 transverse furrow between the posterior end of the median lobe and the 

 connecting ridge joining the third lateral lobes, and the furrow between 

 this connecting ridge and the occipital segment, both are unnaturally 

 deep, and narrow, showing distinct tool marks in some of the casts. 

 Evidently the cleaner thought that these furrows should agree in sharp- 

 ness and depth with the furrows separating the compound anterior 

 lateral lobes from the median and third lateral lobes. In a similar 

 manner, the posterior margin of the occipital segment shows evidence of 

 the cleaners tool, and it is not at all unlikely that in the original of the 

 cast, before cleaning, this segment was subtri angular in outline, as in 

 the Mills quarry specimen here figured. Compared with the latter, the 

 ornamentation on the surface of the cast is much coarser, and there is no 

 evidence of numerous smaller papilla among the coarser pustules; this, 

 however, could scarcely be regarded as a specific distinction, in the 

 absence of other well-marked differences. There is no trace of occipital 

 lobes, nor of any remnant of the anterior border visible in these casts. 



Trochurus hanoverensis, Miller and Gurley (Plate XII, Figs. 2 

 A-D), from the Laurel limestone at Madison, Indiana, was found by 

 rock breakers while repairing the Hanover pike. Compared with 

 Trochurus phlyctainodes, the median lobe is much wider, and its curva- 

 ture from front to rear is more regular, its outline forming almost three- 

 fourths of a circle. There appears to have been a strong spine near the 

 lateral extremity of each of the third lateral lobes. The occipital lobes 

 are low and inconspicuous. The posterior margin of the occipital 

 segment is unknown. 



Trochurus byrneasnus, Miller and Gurley, (Plate XII, Figs. 3 

 A-E), occurs in the Laurel limestone at Madison, Indiana, associated 

 with Trochurus hanoverensis, Sphcercxochus romingeri, and a large 

 Encrinurus pygidium. No Pentamcrus oblongus occurs at this horizon. 

 Trochurus byrnesanus is characterized by a narrow median lobe with 

 subparallel sides; its dorsal outline is nearly straight and anteriorly 

 it is strongly curved downward and backward, the outline between this 

 bend and the anterior border of the cephalon being gently convex. Seen 

 from above, the compound anterior lateral lobes have about the same 

 width as the median lobe, and the transverse furrow limiting the pos- 

 terior margin of these three lobes is almost straight. The lateral 

 extremities of the third lateral lobes are elevated apparently into short 

 spines. Only one side of the occipital segment is preserved and its 

 median termination is unknown. 



