286 Mr. H. J. Carter on known Fossil Sponges. 
assumed ; but in no instance, except the end of a branch of a 
Chalina mentioned, have I been able to find the spicule én sttu, 
that is in the entire structure of which it formed part, and 
this only conjecturally. 
I also noticed the occurrence of sponge-spicules from the 
Carboniferous strata of Ben Bulben in the north of Ireland, 
near Sligo, wherein the chert appears to be composed of them 
in a transitionary state from the entire spicule to a homo- 
geneous mass; also in the Carboniferous of Scotland near 
Glasgow (‘ Annals,’ 1880, vol. vi. p. 209, pl. xiv. B. figs. 1- 
17); but the latter case has been much more elaborately dealt 
with by Dr. Hinde in his paper on the “ Organic Origin of 
the Chert”’ (‘Geological Magazine,’ dec. iii. vol. iv. no. 10, 
p- 435, October 1887), where, at p. 442, he observes that 
in thin slices of this chert and that from other localities 
examined with the microscope by transmitted light, “ it 
is resolved into microscopic spicules, confusedly intermingled 
together, whose individual outlines can be traced with varying 
degrees of clearness.” 
Hence the chert in the Carboniferous period appears to 
indicate a similar condition to that in which it is found in the 
Upper-Greensand detritus at this place (Budleigh Salterton), 
and in the spiculiferous sand-bed at “‘ Haldon Hill” to which 
I have alluded. 
Among the fossil spicules which I have figured (J. ¢.) are 
undoubted forms that originally came from the Monaxonid 
group, ex. gr. the bihamate, Bk. (sigma, R. & D.), no. 43 
(2. c.), which, although it can be seen with the naked eye, 
being 1-400th mech in length, is exceeded by the largest 
existing form that I have observed, viz. in Esperta villosa, 
where it is fully 1-64th of an inch (Journ. Roy. Mier. Soe. 
1879, vol. ii. pl. xviia. fig. 12 6). But while recent specimens 
of the bihamate exceed in length the fossil one that I have 
mentioned, the largest of several tricurvates (toxa, R. & D.) 
that I have just found among other sponge-spicules, chiefly 
Tetractinellid, in a transparent portion of Upper-Greensand 
chert from this locality, measures from 1-16th to 1-7th inch 
in length, the largest recent specimen that I have seen, viz. 
that which I described and figured in 1874 (‘ Annals,’ 
vol. xiv. p. 457, pl. 1. fig. 27), being only 1-60th inch long, 
although in other respects, that is in the straightness and 
length of the arms, relative smallness and abruptness of the 
bow, together with its semicircular form, it closely resembles 
the fossil; moreover, the arms appear to have been spined for 
two thirds of their length. Of the longest specimen only 
about three fourths remain, so that the measurement from 
