Lower Palaeozoic Rocks of the South of Scotland. 43 



consequently very few in comparison with the numbers which 

 may be obtained from a recent ooze or from loose fossil 

 material. 



With two or three doubtful exceptions tlie forms which I 

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

 in one of the four legions or subclasses into which HtEckel 

 has divided tiie Radiolaria, viz. that of the Spumellaria or 

 Peripylea. Within this subclass but two suborders, the 

 lieloidea and the Spha^roidea, are represented. In the first 

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

 consists of numerous solid siliceous spicules irregularly scat- 

 tered in tiie soft structures surrounding the central capsule. 

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

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

 H deckel's ' Challenger ' Report, are abundant in the chert. 

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

 p. b(^) are very similar in form to the spicules of Calcispongcs ; 

 others, however, with a central rod giving otf 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 way as we should expect to be the case if 

 forms like the recent Lampoxanthium pandora^ Ha3ckel *, 

 and Spha'rozoum pandora^ H.t, 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 Sphge- 

 roidea, in which 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. tigs. 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. 



