SCHIZOCxRAPTUS. 71 



very slig-litlj in width from their origin, while the lateral hranehes a])peai- to be of 

 uniform breadth throughout their length. As a general rule the theca3 arc obscure 

 on the whole proximal portion. 



Only two species of Hrhizoyyaplns are at present known— /9. rdicalaias and 

 >S'. tardifnrcatus. 



Schizograptus reticulatus (Nicholson). Plate VI, fig. 7. 



1868. Dichxjrajisus retici(Jalns, NichuLsoii, Qiuirt. Joiirn. Geol. Soc-., vol. xxiv, p. 143, pi. v, figs. 4, 5. 

 1876. Schizofjraptus reticulatus, Nicholson, Gcol. Mag., dec. 2, vol. iii, p. 248. 

 1898. 8cMzo(jrapius retimilaius, Elles, Quart. Journ. Geol. Soc, vol. liv, p. 480. 



Stipes rigid, those of first order short, those of second order about 4 — 7 cm. 

 in length and 1'2 mm. in width, constituting the four main stipes of the 

 polypary ; from each of these, tAvo lateral branches are early given off at a large 

 angle (approximating to a right angle) Avith the axis of the main stipes, and 

 all on the same side. Thecae about ten in 10 mm., inclined at 20°, about 

 1 mm. in length, three times as long as wide ; outer walls straight, over- 

 lapping one quarter of their length. Apertural margin straight, approxi- 

 mately perpendicular. 

 Description. — The first lateral branch is given off at a distance of about 5 mm. 

 from the point of dichotomy, and the second at a distance of 10 mm. from the first. 

 The distance between the two lateral branches is the same on all the main stipes. 

 On one main stipe, whose total length was 70 mm., only two lateral branches are 

 visible, and both of them arise within the first 17 mm. of its length. On no stipe 

 have more than two lateral branches been observed, therefore it Avould seem likely 

 that no more were developed. 



The characters of the tliecas as given above are drawn up from several Jjake 

 District specimens more or less indifferently preserved, and must be regarded as 

 essentially approxim ate . 



Affinities. — S. ret ictihi fits may readily be distinguished from the only other 

 species yet known {S. tdrdi/nrcatiis) by the short space between the point of 

 dichotomy and the point of origin of the first lateral branch. 

 Horizon and Localities. — Arenig, Middle SkiddaAv Slates (P). 

 LaJce District : Scale Hill, Crummock ; Barf. 



Associates, etc. — H. reticulatus has as yet Ijcen only recognised in the Skiddaw 

 Slates, where it is rare. Its associates are unknown. The best specimens are in 

 Postlethwaite's collection. 



10 



