134 Mr. H. J. Carter oji Fossil Sponge-spicules of 



the presence of a few tubercles bore indication of the original 

 appearance ; and these were too indistinct to be of any specific 

 value. 



The largest as to size and general shape, viz. that figured, 

 bears a greater resemblance to those of Geodta Thomsonii^ Sdt. 

 (Atlan. Spong. Faun. Taf. 6. fig. 13), than to any other existing 

 species with which I am acquainted. 



There is hardly a large spicule in the deposit to which one 

 or more of these little balls are not adlierent ; so that, as before 

 stated, this must be regarded as accidental, and arising fi-om 

 their having been thrown together promiscuously at the time 

 the deposit was formed. 



It has, however, been necessary to add one of them to the 

 combination of spicules before mentioned to complete the 

 complement of Geodites haldonensis ; and for this purpose 

 we may take the largest size, or that figured in figs. 55 and 

 oQ. Of course the combination is conventional and provi- 

 sional ; but it is necessary, mider the circumstances, for futm-e 

 reference. 



Before concluding, we have to advert to a structural pecu- 

 liarity in many of these fossil spicules, which finds its illustra- 

 tion in fig. 75, PI. X., and to which I have before alluded 

 as an unusual enlargement of the axial canal. Here it will be 

 observed that the axial canal is extremely wide, and the wall 

 of the spicule therefore veiy narrow, also that the former has 

 in it the end of another spicule and several grains of sand : 

 a is the wall, h h the dilated canal, c c, grains of sand, and 

 d the point of a spicule. 



This fragment, which represents part of the shaft of a 

 ternate-headed spicule, is an illustration of what is frequently 

 met with in the Haldon deposit, and, by the presence of the 

 grains of sand, shows that this condition of the spicule was 

 not produced dm'ing fossilizatiou, but must have existed from 

 the beginning. 



It seems to derive explanation, however, from what I have 

 particularly noticed in the deciduous spicules, both fragmental 

 and entire, of the spiculo-arenaceous sponges and those in the 

 head of SqiiamuUna scojnda (Annals, 1870, vol. v. pi. 4), viz. 

 that most of them have unusually wide canals, insomuch that 

 I have often thought that this arrest of development (for spi- 

 cules appcartobe formed endogenously rather than exogenously) 

 in many instances had led to their being thrown ofi" (like dead 

 feathers) from the sponges in which they had thus become use- 

 less ; and floating about, rather than sinking at once or becom- 

 ing fractured and destroyed like the more solid ones, they 

 had thus been more easily captured by those organisms which 



