530 GEOLOGY OF OHIO. 



The type specimen of Phacops trisidcatus \ Hall, is certainty a closely 

 allied form if not identical. It has 11 segments in the thoracic region, the 

 first three lateral segments of the pygidium are distinct, the fourth is 

 visible, the fifth and sixth are mere fine transverse strise. The first three 

 segments of the medium portion of the pygidium are distinct, the fourth 

 is visible, the fifth is a mere point. It was found in the Clinton at 

 Rochester, New York, and the only distinction so far known lies in the 

 relatively broader p3'gidium, a character which may be due to the state 

 of preservation when found in shales. 



At Brown's Quarry is found a pygidium suggesting affinities with 

 Dalmanites, with three pleural segments distinct, the groove along their 

 upper line being better shown in a cast of the lower side than on the 

 upper surface of the original. The fourth and fifth segments are indis- 

 tinct. The sixth and seventh can barely be made out, and an eighth segment 

 is perhaps possible. The striking feature of this pygidium consists in its 

 broad concave border. The pygidium is 5 mm. long as far as the termination 

 of the axial region; including the border it measures 6.5 mm; the border is 

 inclined and is almost 2 mm. broad. The width of the pygidium is 

 about 7.3 mm. minus the border, but including the latter it measures 9.0 

 mm. The folds of the pleural segments descend as indistinct wrinkles 

 upon this border, and posteriorly a narrow ridge or elevation descends 

 from the axial region to about the middle of the border. The posterior 

 margin is perfectly rounded, and has no trace of posterior prolongation. 

 A voxy shallow but distinct groove separates the border from the remain- 

 der of the pygidium. 



The p3^gidium figured from the Soldiers' Home is similar but not iden- 

 tical. The groove defining the broad border from the remainder of the 

 pygidium is not present, the pleural segments descend to within a short 

 distance of the margin, there is no distinct border, and while a broad 

 shallow groove runs along the margin posteriorly this is distinct only 

 along the posterior half of the pygidium (Plate 27, fig. 4.) 



A much smaller pygidium from the " Orthoceras block" found at 

 Huffman's Quarry shows features identical with the last though it is 

 much smaller: 6 mm. wide and 4 mm. long. There is a sort of elevation 

 running posteriorly from the axial region to the border. 



The rounded posterior borders of these specimens suggest affinities 

 with Phacops. The Soldiers' Home and Huffman Quarry specimens, 

 especially the latter, resemble the pygidia usually associated with Phacops 

 trisulcatus. The first described pygidium from Brown's Quarry, if not 

 identical, belongs possibly to a closety allied species. It is well known 

 that the genera Phacops and Dalmanites are closely allied. 



Dalmanites Wcrthneri, Foerste. 



(Plate 27, Figs. 22 22a, 23, 24, 25.) 



This species was described in the Bulletin of Denison Uuiversity 

 Vol. I, and figured in Vol. II, from the upper third of the limestone at 



