142 BRITISH PALAOZOIC SPONGES. 
state, and owing to the fragile manner in which the spicules are held together in 
the existing species, their preservation as fossils in their normal positions can 
hardly be expected. Detached spicules closely resembling in form those of existing 
examples of the genus, but for the most part of larger proportions, are, however, 
of not infrequent occurrence in Carboniferous and newer strata, and they may 
provisionally be ranged in this genus. 
I have followed Vosmaer in regarding O. Schmidt as the author of the genus, 
since he not only modified Nardo’s original name, but was the first to define the 
characters of the Sponges assigned to the genus. 
19. Rentera Cartert, Hinde. Plate IV, figs. 5, 5a—5f. 
1879. Sprcute or « Renrerrp Sponer, Carter. Ann. and Mag. Nat. Hist., ser. 5, 
vol. iii, p. 144, pl. xxi, fig. 11. 
1883. Renrera? Carrert, Hinde. Cat. Foss. Sponges, p. 19, pl. i, fig. 8. 
The detached spicules on which this species is based are smooth, cylindrical, 
gently arcuate, or with a nearly straight central portion and somewhat abruptly 
incurved extremities, which in all cases are obtusely rounded. They range from 
‘8 to 2°5 mm. in length and from -11 to *22 mm. in thickness. There are numerous 
gradations between the extreme forms, which indicate that they probably all belong 
to a single species. 
The spicules are now composed nearly entirely of chalcedonic silica; in a few 
instances the silica is crystalline. They are now usually solid throughout, in only 
a single example of those which have come under my notice has the axial canal been 
preserved. They are fairly abundant and well preserved. 
Distribution.—Lower Carboniferous: Upper Limestone series at Glencart, 
Dalry, Ayrshire. 
20. Rentera scrruLa, Hinde, sp. nov. Plate IV, fig. 4. 
1880. Rentera? Carter. Ann.and Mag. Nat. Hist., ser. 5, vol. vi, p. 212, pl. xiv, 
fig. 14. 
The spicules included in this species are cylindrical, smooth, gently arcuate, 
and with evenly rounded extremities. They vary from*5 mm. to ‘9 mm. in length, 
and from ‘09 mm. to‘15 mm. in thickness. They are now partly of chalcedonic and 
