Vol.51.] RADIOLARIAN ROCKS IN THE LOWER CULM MEASURES. 635 



but it is very seldom that more than three rays are visible, and these 

 appear to be nearly in a plane. The rays may be either simple and 

 of uniform thickness as in fig. 1 g, or swollen at the ends to a bulb 

 or knob as in figs. 1 c, d, e,f, or they dichotomize and each branch 

 becomes lobed as in figs. 1 a, b. They vary considerably in size ; a 

 small form is - 03 mm., and a large one '0^5 mm. in width. They 

 are generally distributed, and have been recognized at Heddon, 

 Swimbridge, and Kent's Hill in North Devon, at Carzantic near 

 Launceston, and at Ramshorn Down and Winstow Lodge near 

 Chudleigh. Rust has figured a form resembling our fig. a from the 

 Silurian of Cabrieres, and he states that the spicules are very 

 abundant in the Devonian and Carboniferous radiolarian rocks 

 of the Southern Ural (' Palaeontographica,' vol. xxxviii. p. 133, 

 pi. viii. fig. 11). 



Order SPH^iroidea, Haeckel. 



Genus Cenosph^ra, Ehrenberg. 



The test is a simple latticed sphere, without radial spines. It is 

 probable that most of the rounded casts, abundant in nearly every 

 microscopic section of these rocks, belong to forms of this genus. 

 They vary in diameter from *065 to "275 mm. It is only excep- 

 tionally that anything beyond the mere outline of the cast is shown 

 in these forms. 



Cenosphcera pachydermia, Riist. PL XXV. fig. 2 (' Palaeonto- 

 graphica,' vol. xxxi. 1885, p. 286, pi. xxvii. figs. 2, 3). The test is 

 •165 mm. in diameter and about '015 mm. in thickness, and the 

 apertures in it are also *015 mm. in width. From Ramshorn Down. 

 Riist states that this form is present in all Palaeozoic radiolarian 

 deposits, as well as in many of those of Jurassic and Cretaceous 

 age. 



Cenosphcera sp. a. PL XXV. fig. 3. Test relatively large, ranging 

 to - 27 mm. in diameter and *03 mm. in thickness ; the apertures are 

 about *022 mm. in width. This form is near to C. ingens, Riist 

 (' Palaeontographica,' vol. xxxviii. p. 1 34, pi. vi. fig. 8), but the walls 

 are distinctly thicker. It is common at Ashbrittle, West Somerset. 



Genus Carposphjsra, Haeckel. 



The test consists of two concentric spheres connected by rays. No 

 radial spines. 



Carposphcera sp. a. PL XXV. fig .4. The outer test is 44 mm. 

 in diameter, and the inner # 05 mm. Neither the connecting rays 

 nor the lattice-structure has been preserved. A form of nearly 

 similar proportions occurs in theMullion Island chert (Quart. Journ. 

 Geol. Soc. vol. xlix. 1893, p. 216, pi. iv. fig. 2). Ramshorn Down. 



Carposphcera sp. b. PL XXV. fig. 5. The outer thin tost is 



