May, 1919] Silurian Fossils From Ohio 391 



the glabellar furrows are distinct; neither of these features 

 is seen in Proetiis collinodosus. 



Encrinurus cf . ornatus Hall and Whitfield. 

 Plate XVIII, Figs. 2 A-C. 



Only a fragment of a cranidium is known. Its length along the 

 middle is estimated at 7 mm., and its width, to the end of the genal 

 angles, but not including the genal spines is estimated at 22 mm. 

 The length of the genal spines is 5 mm. Conspicuous tubercles 

 occur on the glabella, on the more strongly- convex part of the 

 cheek which surrounds the eye, and on the marginal rim. On the 

 depressed part of the free cheek, toward the genal angle, the tubercles 

 are inconspicuous. In front of the series of conspicuous tubercles 

 on the free cheeks there is a much less conspicuous series of smaller 

 tubercles. Near the genal angles, one or two tubercles occur also on 

 the posterior border of the free cheek and on the genal spine. 



The pygidium is obovate-triangular. Its width is 14 mm., and its 

 length, in its present state of preservation, beginning with the anterior 

 margin of the first annulation, is 17 mm. The posterior end apparently 

 tenninated in a short spine extending only slightly beyond that part 

 at present remaining. The length of the axial lobe is 14.5 mm.; anter- 

 iorly this lobe is crossed by two annulations, the second of which bears 

 a median tubercle. Posterior to the second annulation the median 

 part of the axial lobe, for about one-fourth of its width, tends to be 

 smooth, the annulations being distinct only along the sides of the lobe. 

 It is rarely possible to count more than 30 annulations, those at the 

 posterior end being indistinguishable, but in remarkably well preserved 

 specimens, in which even the terminal annulations are distinct, as 

 many as 36 may be counted. 



In the figured specimen, tubercles occur on the median parts of the 

 axial lobe, at annulations 2, 5, 9, 14, 20, 25, 30?, and ?, the number 

 of the annulations bearing the last two tubercles being uncertain. 

 In a second specimen, tubercles occurred at 2, 5, 9, 14, 19, the location 

 of the remainder being uncertain. In a third specimen, tubercles 

 occurred at 2, 5, 9, 13, 18, 22, 26?, and ?, the location of the last two 

 being uncertain. In a fourth specimen, tubercles occurred at 2, 6, 9, 

 13, 18, 24, 29, and 33, the axial lobe terminating with the thirty-sixth 

 annulation. That the location of even the first four tubercles may 

 vary is shown by a fifth specimen, in which they occurred at 2, 4, 7, 

 12, 16, 21, and ?, the location of the last being uncertain. These 

 observations indicate to what an extent the exact location of the tubercles 

 along the median line of the axial lobe varies, and of how little value 

 their location is in the discrimination of species. In general, it may be 

 stated that seven tubercles may be counted frequently along the axial 

 lobe of the species here described, and that an eighth tubercle may be 

 recognized on the better preserved specimens. 



There are eight pairs of pleural ribs. The distal parts of these 

 ribs, about 4 or 5 mm. from their ends, cur\^e strongly downward and 



