Lower Palceozoic Rocks of the South of Scotland. 55 



Bd. xxxi. p. 289), but in a subsequent memoir they are con- 

 sidered as Discoidea under the modified name Triactis 

 (Palfeontogr. Bd. xxxir. p. 197). Hseckel* has referred 

 other discoidal three-spined forms to the genus Triactiscus. 

 So far as I can ascertain no spherical "spongy" forms with 

 a medullary shell and three radial spines, as in the proposed 

 genus, have as yet been described. It is difficult to ascertain 

 with absolute certuinty now that these minute shells are 

 imbedded in the solid chert whether particular specimens are 

 discoidal or spherical ; but their outlines are uniformly cir- 

 cular, and if discoidal shells had been present one would have 

 expected to meet with lenticular or elliptical forms in the 

 rock-sections. 



Trijyosphcera PeacJiii, sp. n. (PI. IV. fig. 9.) 



Shell approximately spherical, the reticulate framework 

 close. The radial spines nearly twice as long as the diameter 

 of the test, straight or curved, tapering gradually, inequi- 

 distant from each other. In no specimen are all the spines 

 intact, but they appear to have been equal in length origi- 

 nally. The medullary test is not shown in the specimen 

 figured owing to the dark infilling, but it is present in others. 

 Diameter of shell '18, of medullary test '05 ; length of spines 

 •42, basal thickness '02 millim. This species is named after 

 B. N. Peach, Esq., F.G.S., of the Geological Survey of 

 Scotland, to whom I am indebted for the opportunity of 

 studying these fossils. 



Distribution. Abington, Lanarkshire ; Broughton Heights, 

 Peeblesshire. 



Triposphmra hastata, sp. n. (PL IV. fig. 2.) 



Shell of close framework, with minute pores ; surface 

 uneven and rough, as if with minute blunt spines. The 

 medullary test in the specimen figured is indicated by a light 

 central space. Spines straight, robust, nearly twice as long 

 as the diameter of the sphere, inequidistant from each other. 

 Only one is preserved intact in the specimen figured, the other 

 two are indicated by their stumpy bases. Diameter of sphere 

 •27, of the medullary test '055 j length of spines '5, basal 

 thickness '025 millim. 



Distribution. Near Abington, Lanarkshire. 



Triposphcera densa^ sp. n. (PI. IV. fig. 10.) 

 Surface of shell nearly even, the three radial spines slender, 

 * Chall. Rep. pt. i. p. 432. 



