154 IP. W. Dodge — Lower Silurian Graptolites. 



only sixteen in an inch, six in ten millimeters. D. longissimus 

 Ivurck * (Upper Silurian) has seven hydrothecse in ten milli- 

 meters ; they overlap each other more than do those in the 

 Maine specimen, and terminate differently. D. foliaceus 

 Murch.,f has eighteen to thirty in an inch, and is wider. D. 

 euglyphus Lapw.,^: for which a different marginal angle of 

 the hydrothecse is stated, has eighteen to twenty-four. D. 

 rugosus Emmons § has twenty and a wider polypary. D. pris- 

 tis has nine or ten in ten millimeters and has a small radicle. || 

 The Maine specimen agrees nearly with D. pristis and D. lon- 

 gissimus in the angle between the outer margin of the hydro- 

 thecse and the central line of the polypary. It has a radicle 

 two millimeters long. 



The precise level at which this probably new species occurs 

 relatively to the other specimens has not yet been ascertained. 



■i. Oraptolithus marcidus Hall, has been treated as identical 

 with Oryptograptus tricornis Carr. (sp.). Prof. Hall's figure 

 shows no essential difference. G. tricornis has parallel lateral 

 margins. In all distinct and entire specimens, from fifteen to 

 forty millimeters long, that I have seen, from Hudson River 

 valley localities, there is well marked distal convergence of 

 the margins. The convergence sometimes begins or becomes 

 more rapid at a point distant perhaps six times the maximum 

 width of the polypary from its proximal extremity, that is 

 about one-half or one-third of its length, and thus is seldom 

 conspicuous in the proximal half of the polypary. A slight 

 proximal convergence also is frequently or usually noticeable. 

 Prof. Hall's figure may represent a specimen which had lost 

 part of its polypary. The few parallel-margined New York 

 specimens that I have seen are small (with pointed distal ex- 

 tremity^) or imperfect. 



I think 0. marcidus should be retained for the present. 



The Maine specimen is from the same piece of shale with 

 the Diplograptus above mentioned (JS"o. 3.) The slightness of 

 the test characteristic in Oryptograptus makes the specimen in- 

 conspicuous, but it is easily recognizable after the attention is 

 directed to it. 



5. The specimens of Glossograptus were obtained from the 

 same ledge as 'No. 1, but from a higher layer of shale. They 

 are very indistinct. The spines appear to be in number about 

 ten on each side. The polypary, exclusive of the spines, is 



* Geol. For. i Stockholm Forh., Bd. vi, Heft 7, p. 302, taf. 14, figs. S, 9. 

 f Sil. Syst., PL xxvi. f. 3. Hopkinsou aud Lapworth in Quart. Journ. Geol. Soc. 

 Lond. 1874, xxxi, p. 657. 



% Ann. and Mag. Nat. Hist, (5) v, p 166. 



§ American Geologist p. 105, PI. 1, fig. 26. 



I Tullberg, op. cit., p. 10. 



17 Like fig. 17, Plate B, of Graptolites of the Quebec Group. 



