Vol. 54.] 



FAUNA OF THE SKIBDAW SLATES. 



487 



Mr. Postlethwaite's collection there is a very prolonged ' elation ' 

 up the stipes, but this is not so pronounced in other specimens. 



The stipes are 

 narrow at their pjg^ 11.— Tetra^raptws Headi {coll, 



ongm, but widen to PosUethwaite). 



a maximum of fully 

 ^2 inch (2'] mm.) 

 when the thecee are 

 seen. The greatest 

 length observed is 

 4| inches (12-2 cm.). 



The thecae num- 

 ber twenty-four in 

 the space of an inch 

 (nine to ten in 

 10 mm.) ; they are 

 long curved tubes, 

 and are inclined at 

 an angle of about 

 40°; their apertures 

 are situated ob- 

 liqaely to the gene- 

 ral direction of the 

 stipe. 



There is another 

 specimen in the 

 Woodwardian Mu- 

 seum which has 

 been referred to 

 T. alatus (Hall). 

 It is a small speci- 

 men, only two stipes 

 are seen, and these 

 do not exceed ^ 

 inch (12-7 mm.) 

 in length. The disc 



is square and straight-sided, and measures ^ inch (8*5 mm.) across 

 each diameter. The membrane certainly does appear to envelope 

 the stipes more or less completely, but I think that this must also 

 be the case in young forms of Tttragraptus Headi. 



The specimen is preserved so as to show the apertures of the 

 thecae facing the observer, and these number twenty-four to the inch 

 (nine to ten in 10 mm.). Taking into consideration the form of the 

 disc and the number of thecse to the inch, I am inclined to think 

 that this specimen is a young form of Tttragraptus Headi. 



Occurrence. — The specimen in Mr. Postlethwaite's collection 

 occurs on a slab on which there are also present Didymograptus 

 patulus (Hall) and D. gihherulus, Nich. ; it belongs probably to the 

 upper part of the Middle Skiddaw Slates. 



Localities. — South-western end of Eandal Crag, Skiddaw. 

 Nicholson also records a specimen from Barf, near Keswick. 



[Nat. size.] 



