Vol. 54.] 



FAUNA OF THE SKIDBAW SLATES. 



495 



Specimen and 

 Locality. 



A. Randal Crag 



B. 1. 



B.2. 



B.3. 



0. 



D. 



E. 



F. 



2 



Barf 



One 

 i slab 1 



69. Oaterside 



76. Bassentliwaite Sand- 

 beds 



Length, 



Width 



(Max.).* 



2 



H 



7 



1 



1 



:? 



14 



1 



1 



mm. 

 31-7 

 57 

 50-6 

 38 

 31-7 

 14-7 

 25-4 

 8-7 

 341 

 25-4 

 25-4 



m. 

 i 



3 



1. 



4 



mm. 

 8-7 

 6-3 

 6-3 

 7 



6-3 

 4-76 

 8 



4-76 

 6-3 

 6-3 

 8-7 

 8-7 



10-5 



No. of 





thecEe 



No. in 



to inch. 



10 mm. 



24 



9-10 



24 



9-10 



24 



9-10 



26 



10 



26 



10 



26 



10 



24 



9-10 



24 



9-10 



26 



10 



24 



9-10 



24 



9-10 



24 



9-10 



24 



9-10 



The species appears to be characterized by (1) the number of thecee 

 in a given unit of length ; (2) the form of the aperture, which is 

 equally extended at its upper and lower limits. 



The thecse are curved throughout the whole length of the rhab- 

 dosoma ; they go out nearly horizontally in the proximal part, but 

 curve back so that the aperture points downwards. The degree 

 of curvature seems to vary somewhat, according to the aspect in 

 which the rhabdosoma is viewed. The curvature is less in the 

 middle of the stipe, and the line of the aperture becomes parallel 

 to the general direction of the rhabdosoma ; above this, the 

 aperture becomes inclined, and the thecse are inclined at a higher 

 angle, which increases steadily towards the distal end, so that 

 eventually in some forms the apertures of the cells lie almost 

 perpendicular to the general direction of the rhabdosoma, a com- 

 plete change in position having thus been effected. The thecae 

 number between twenty-four and twenty-six to the inch (nine to 

 ten in 10 mm.) ; they never exceed twenty-six, and are far more 

 commonly twenty-four. They are in contact throughout their 

 length, and have slightly mucronate apertures. 



The proximal end is not often well preserved, but two specimens 

 show some details. In one the sicula and first theca can be made 

 out; the sicula has a length of about J-g- inch (1-58 mm.); the 

 first theca seems to be developed from near its apex, and closely 

 resembles it in general form. Another specimen shows a view 

 resembling that figured by Holm (op. cit. pi. xiii, fig. 2). 



The larger forms of this species bear a superficial resemblance to 

 Phyllog vastus angustifolius, but are always broader, and the form 

 of the aperture is distinctive. 



Occurrenc e. — With Didymograptus gihherulus, Mch., D. nitidus 

 (Hall), Azygograptus suecicus, Moberg, Pliyllograptus angustifolius, 

 Hall, Dichograjptus octohracliiatus (Hall). It appears to be very 



* In some specimens the maximum width is quite near the proximal end, 

 in others it is nearer the middle of the rhabdosoma. 



Q. J. G. S. No. 215. 



2m 



