286 Mr. H. J. Carter on hnown 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 in situ, 

 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 transitionarj state from the entire spicule to a homo- 

 geneous mass ; also in the Carboniferous of Scotland near 

 Glasgow (' Annals,' 1880, vol. vi. p. 209, pi. 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 Mag'azine,' 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 {I. c.) are 

 undoubted forms that originally came from the Monaxonid 

 group, ex. gr. the bihamate, Bk. (sigma, R. & D.), no. 43 

 {I. c), which, although it can be seen with the naked eye, 

 being l-400th inch in length, is exceeded by the largest 

 existing form that I have observed, viz. in Esperia villosa, 

 where it is fully l-64th of an inch (Journ. Roy. Micr. Soc. 

 1879, vol. ii. pi. xvii a. fig. 12 b). 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 l-16th to l-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, pi. i. fig. 27), being only l-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 



