168 Mr. C. Lap worth on new British Graptolites. 



Climacogr •aphis , the subperpendicular margin and deep exca- 

 vation. In the reverse aspect (figs. 25 e, 25 f) the theca? are 

 those of Diplograptus, with long inclined subparallel walls 

 and oblique apertural margin ; while the central part of the 

 polypaiy appears similarly destitute of the longitudinal sep- 

 tum. In the obverse aspect of the examples presented in 

 relief, or but slightly compressed, the under wall of each 

 hydrotheca is continued in a deeply impressed line, which 

 crosses the face of the polypaiy obliquely till it meets with a 

 similar line derived from the corresponding hydrotheca of the 

 opposite series (figs. 25 a, 25 b-25 <1) . Thus the base of each 

 hydrotheca appears to rest upon the lower half of the upper 

 wall of its opposite neighbour. A longitudinal septal line 

 formed by the deep groove between these opposed hydrothecoe 

 runs in short zigzag curves down the middle third of the 

 polypaiy, as in Idiograptus and in the Retiolitida? generally. 



The American species Diplograptus amplexicaulis, Hall 

 (Pal. New York, vol. i.), clearly belongs to the same 

 subgroup. It differs from the present form chiefly in the 

 greater length and tenuity of the polypaiy, and in the form 

 of the distal portions of the hydrotheca?. (See Hall, 20th 

 Report State Cabinet, 1867, pi. iii. figs. 6 & 7.) 



Diplograptus perexcavatus is a common fossil in the Glen- 

 kiln beds of Scotland and Ireland, and in the Upper Llandeilo 

 strata of Llandrindod Wells, Radnorshire. 



25. Diplograptus rugosus, Emmons ? 



Diplograptus rugosus, Emmons, American Geology, pi. i. fig. 26. 



Diplograptus laciniatus, Emmons, ibid. fig. 24. 



Diplograptus {Graptolithus) pristis, Hall, Pal. New York, vol. i. pi. 72. 



fig. 1, o, &c. 

 Diplograptus hypniformis, White, Geol. Rep. 100th Meridian. 



Polypaiy diprionidian, one to two inches in length, margins 

 parallel distally, but tapering proximally from an average 

 diameter of about one eighth of an inch to a blunt initial ex- 

 tremity, which is invariably provided with a well-marked 

 radicle and lateral spines. Virgula stout, prolonged distally. 

 Hydrotheca? twenty-four to twenty-eight to the inch, short 

 stout tubes, inclined at an angle of about 40°, slightly over- 

 lapping, deeply excavated; apertural margin straight or con- 

 cave, usually greatly inclined ; denticle acute. Test striated. 



The peculiarities of the hydrotheca? constitute the most 

 pronounced characteristic of this species. In the living state 

 they were probably short stout tubes, slightly overlapping, 

 and greatly narrowed transversely, but with a broad expanded 

 aperture. In the profile view they are seen to be flattened 



