GEODITES. 149 



are but poorly preserved. I have been unable to detect any of a vermiform figure 

 as represented by Mr. Carter. 



This species differs from E. Armstrongs in its mode of growth, in the more 

 robust character of the fibres, and in the somewhat greater thickness of the 

 spicules. 



Distribution. — Carboniferous : Upper part of Lower Limestone series ; Cun- 

 ningham Baidland, Law Quarry, Dairy, Ayrshire. 



Sub-Order. — Tetbactinellid^i. 



Genus. — Geodites, Garter. 



1871. Annals and Mag. Nat. Hist., ser. 4, vol. vii, p. 129. 



Generic Characters. — Sponges consisting of skeletal-spicules with bifid or trifid 

 summit-rays and elongated shafts, and also of large acerate spicules and a dermal 

 layer of minute globate or reniform spicules. 



No formal definition of this genus was given by Mr. Carter, who proposed it 

 to include detached spicules of the forms indicated, which are similar to those 

 present in the existing genus, Geodia, Lam., and, with the exception of the 

 dermal globular spicules, in Stelletta, Schmidt, and other allied genera. As the 

 differences which characterise the recent genera of this group (of which Geodia 

 may be accepted as the representative form) cannot be recognised in the detached 

 fossil spicules, it seems preferable to adopt for them the common generic term 

 proposed by Mr. Carter. 



The acerate spicules in different species of this genus vary but little in form, 

 and no satisfactory distinctions can be based on their relative proportions ; but the 

 characters of the bifid and trifid spicules appear to be sufficiently constant to 

 permit specific distinctions to be based on them. 



Owing to the fragile manner in which the spicules of this group of Sponges 

 are held together by perishable spongin, it is extremely rare to find them in their 

 natural positions in the fossil state, and their occurrence can only be recognised 

 from the detached spicules. These make their first appearance in the Lower 

 Carboniferous of Ayrshire; they occur also in the Lias of the Tyrol, and are 

 extremely abundant in the Cretaceous strata of Britain and Germany. 



