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NEW YORK STATE MUSEUM 



the correspondingly great relative width of the middle face of the rhabdo- 

 some, as well as the close arrangement of the thecae are the most charac- 

 teristic features of this mutation. From the associated forms in the Utica 

 shale it is readily distinguished by these characters and from 

 D. peosta, with which it is associated in the Lorraine beds, 

 by the greater width attained and its more gradual widening. 



Diplograptus crassitestus sp. nor. 



Plate 25, figure 6 



Description. Synrhabdosome not observed. Rhabdosomes 

 with thick test and of large proportions, length of largest (incom- 

 plete) specimen 41 mm, its width 2.2 mm at one extremity and 

 1.8 mm at the other, and 3 mm in another specimen ; very gradu- 

 ally widening, quadrilateral in section, with the lateral faces twice 

 as wide as the frontal ones. The lateral faces smooth, both 

 slightly concave and with a faint median sutural line. Sicula not 

 observed. Sicular end narrow (.6 mm wide), furnished with a 

 small virgella (2 mm long). Thecae numbering 7 to 10 in 10 mm 

 (18-25 in 1 inch), three times as long as wide, sub- 

 rectangular in section, overlapping one third their 

 length ; inclined at an angle of 30 to 40, the outer 

 margin straight, often convex, impressed or even exca- 

 vated (especially in the older thecae) in the proximal 

 part; aperture perpendicular to axis, apertural margin 

 straight or slightly concave, occupying one fourth the 

 width of the rhabdosome. Nemacaulus thick, mostly 

 short. 



Formation and localities. Sylvan shale, Arbuckle 

 mountains, Indian Territory. Collected by Dr E. O. 

 Ulrich, who informs me that the Sylvan shale is 

 younger than the Richmond beds. 



Remarks. This species is, of the eastern American varieties of 

 ]). foliaceus, most nearly related to D. foliaceus van incisus 



299 



300 



Fig. 299, 300 Diplograp- 

 tus crassitestus sp. nov. 

 Fie;. 299 Young rhabdosome. 

 Fig. joo Portion of mature 

 rhabdosome. (x 5) 



