170 Mr. C. Lapworth on new British Graptolites. 



ing towards a rectangular aperture, which is furnished with 

 two distinct thecal spines. Periderm continuous, of great 

 tenuity, apparently strengthened by an outline skeleton of 

 strong chitinous threads. 



The above title is proposed for a group of spinose diprio- 

 nidian Graptolitidaj that differ in several marked respects from 

 Diplograptus foliaceus (Murch.) audits allies. They resemble 

 Lasiograptus and the Retiolitidse in the great tenuity of the 

 periderm, and in the fact that when the latter is indifferently 

 preserved, as is frequently the case, all that remains of the 

 fossil is an outline of chitinous threads, giving it all the ap- 

 pearance of a skeleton Betiolites. The section of the polypary 

 appears to have been concavo-convex ; and in the normal view 

 the two series of hydrothecse are seen to have their bases in 

 contact, as in Betiolites and Lasiograptus, a strong separating . 

 chitinous thread marking the place of the zigzag septum. In 

 both the species known the aperture is provided with two 

 spines, which proceed from the sinuses of the quadrangular 

 orifice, and have a somewhat ascending direction. This sub- 

 genus points in the direction of Hallograptus, Carruthers, 

 MS. (of which Diplograptus (Hallograptus) bimucronatus, 

 Nich., may be regarded as the type), but differs from it most 

 distinctly in the absence of the scopulate reproductive processes 

 which mark the gonosome in that genus. Hall figures a form, 

 which he refers to his Diplograptus (Idiograptus) Whitfieldi, 

 with scopulae (Grapt. Quebec Group, pi. v. figs. 6-10) ; but 

 this form is clearly distinct from his original D. Wkitjieldii 

 (Pal. New York, vol. iii. fig. 516), and is, I doubt not, a true 

 Hallograptus. 



27. Idiograptus (Diplograptus) acideatus, sp. nov. 

 (PI. VI. figs. 23 a-23f.) 



Polypary about one inch in length, gradually augmenting 

 in diameter, from a triangular proximal extremity to a maxi- 

 mum width of about one twelfth of an inch. Virgula distally 

 prolonged. HydrothecEe twenty-four to twenty-eight to the 

 inch, alternately arranged, and provided with well-marked, 

 slightly ascending, apertural spines. 



The bluntly triangular proximal extremity of the polypary 

 in this species is destitute of any extraneous ornamentation 

 beyond the normal apertural spines of the primary hydrothecse, 

 which hardly exceed their ordinary length. The distal ex- 

 tremity of the polypary is formed by the final thecaj, and 

 shows four distinct spines projecting from its angles. The 

 virgula is filiform and straight, and is prolonged for a distance 

 equal to about half the length of the polypary itself. There 



