Loicer Pahvozotc Rocks of the South of Scotland. 43 



consequently very few in conij)ari.<on with the numbers wliich 

 mny be obtained troni a reeent ooze or from loose fossil 

 nuiterial. 



A\'ith two or tinee doubtful exceptions the forms which I 

 have been able to determine in this chert may be all incliideil 

 in one of the four legions or subclasses into which lltiickel 

 has divided the Kadiolaria, viz. that of the Spumeliaria or 

 Peripylea. Within this subclass but two suborders, tlie 

 Beloidea and the Sphceroidea, are represented. In the first 

 of these there is no connected siliceous test ; but the skeleton 

 consists of imnierous solid siliceous spicules irregularly scat- 

 tered in the soft structures surrounding the central capsule. 

 Spicules of similar form and proportions to those of the exist- 

 ing members of this grouj), represented in plates ii. and iv. of 

 lla^ckel's 'Challenger' Report, are abundant in the chert. 

 Some of them with three- or four-pointed rays (woodcut, a-f, 

 p. 56) are very similar in form to the spicules of Calcisponges ; 

 others, however, Avith a central rod giving off divergent rays 

 from its extremities (woodcut, g) are quite distinct from any 

 known type of sponge-spicule. These detached spicules 

 are in the same condition as the lattice-like Radiolaria with 

 which they are intermingled, and there can be no doubt that 

 like these latter they were originally siliceous. Though now 

 detached from their normal positions, the inevitable result of 

 the decay of the soft structures, yet instances are not unfre- 

 quent in this chert where several of these Beloid spicules 

 occur in close proximity to each other, forming small groups, 

 much in the same Avay as we should expect to be the case if 

 forms like the recent Lampoxanthium pandora^ Hseckel *, 

 and Sj)hcerosoum pandora^ H.f, were fossilized under favour- 

 able conditions. 



The great majority of the Radiolaria in this chert, how- 

 ever, belong to the more normal types of the suborder Spha3- 

 roidea, in whicii the test consists of one or more rounded shells 

 with a lattice-like or irregularly reticulate, so-called "spongy*' 

 structure. The simplest forms of these, in which the test is 

 without spines or with only very minute secondary spines, 

 are comparatively rare (PI, III. figs. 1, 2). Tests in which 

 there is a single large radial spine, with or without secondary 

 spines, are abundant. In some the outer or cortical test con- 

 sists of simple lattice-like structure with subcircular or irre- 

 gular meshes (PI. III. figs. 3, 4, 5, PI. IV. fig. 3) ; in others 

 the structure is " spongy ■" (PI, III. fig. 7), whilst in another 

 genus with the same structure there is a concentric inner or 

 medullary test (PI. III. figs. 8, 9). Shells with three or with 



* Chall. Report, pi. ii. fig. 1. t Ihid. pi. iv, fig. 6. 



