Lower Palaeozoic 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 
(Palaeontogr. Bd. xxxiv. p. 197). Haeckel* has referred 
other discoidal three-spined forms to the genus Triactiscus. 
So far as I can ascertain no spherical u 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 certainty 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. 
Triposphcera Peachii , 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 T8, 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. 
Triposphcera hastata 7 sp. n. (PI. 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 ; length of spines *5, basal 
thickness *025 millim. 
Distribution . Near Abington, Lanarkshire. 
Triposphcera densa y sp. n. (PI. IV. fig. 10.) 
Surface of shell nearly even, the three radial spines slender, 
* Chall. Rep. pt. i. p. 432. 
