Vol. 54.] 



EATUSTA OP THE SKIDDAW SLATES. 



481 



Postlethwaite). 



[Nat. size.] 



measaring together ^\ mch (2-1 ^- 7.-Schizograptus 



mm.); four stipes ot the 2nd f,,,catus, so. nov. 



order are developed irom these as 



a result of dichotomous division. 



These constitute the main stipes 



of the rhabdosoma. On each main 



stipe, at a distance of -^-^ inch (14-7 



mm.) from the point of dichotomy, 



the first lateral branch is given off 



at an angle of about 70° ; a second 



lateral branch at a similar angle, at 



a distance of ^ inch from the first 



(8-5 mm.) ; and a third at the same 



angle, and at a similar distance. 



There seems to be no further 



branching. 



The length of the stipes is 1| to 

 2 inches (44 to 50 mm.), and the 

 maximum width is -^-L- inch (1*05 

 mm.). 



All details regarding the thecse 

 are obscure, but they number twenty 

 to the inch (eight in 10 mm.), are in 

 contact for about half their length, 

 and have oblique apertures. 



The species differs from ScMzograptus reticulatus, 



(1) In having three branches of the 3rd order, and 



situated closer together ; 



(2) In lateness of development of the lateral branches. 

 Locality. — Carlside Edge. 



Genus Pleurograptus, Nich. 



Plbtjkograpifs vagans, Nich. 



1868. Pleurograptus vagans, Nicli. Qaart. Journ. Geol. Soc. vol. xk\v, p. 

 pi. vi, figs. 4 & 5. 



The specimen is only a fragment, but it seems to be iden 

 with that figured 



by Nicholson (op. Eig. 8. — Pleurograptus vagans 



cit. fig. 4). It shows {coll. Postlethwaite). 



a main stipe giving 

 off a number of 

 simple lateral stipes 

 at an angle of 

 about 60^ These 

 are given off at 

 irregular intervals, 

 and from one side 

 only ; as many as 

 ten may be count- 

 ed, but of these 

 only two show the 



2l2 



tardi- 



{coll. 



these 



144, 

 tical 



[Nat size.] 



