_ 46 - 



blance in the spicules of the recent sponges and those from 

 the Horstead flint. Beyond the differences in the state of 

 preservation there is scarcely anything to distinguish the fossil 

 Chalk spicules from those of the existing sponge, P. amyg- 

 daloides which was dredged from a depth of 292 fathoms near 

 Cape S' Vincent. 



Similar spicules, as regards form, have been found in 

 the Irish Chalk (Wright: op. cit. PI. II, fig. 7 a, b) in West- 

 phalia (Ueber Coelop. Taf. V, figs. 54,' 55) and also in the 

 Eocene Sand of Brussels (Rutot : op. cit. PI. Ill, fig. 8). 



Pachastrella Carteri, n. sp. 



(Plate in, figs. 29, 30, 31). 



Simple quadrifid spicules, with short robust, cylindrical 

 or conical, and obtusely rounded arms, forming a depressed 

 pyramid with a short arm at the apex. In figs. 29 and 3 1 , the 

 stout conical blunted arms vary from 0,47 mm. to 0,67 mm. in 

 length, and are 0,225 J^f"- ^^ thickness. In the more regular spicule 

 (fig. 30) the arms are cylindrical and measure 0,337 "I!"- by 

 o, 1 1 2 mm. These spicules appear intermediate between those forms 

 of skeleton spicule with long pointed simple arms of which P. atnyg- 

 daloides, Carter is the type, and those in which one or more of 

 the arms are bifurcated at the extremities as in the recent 

 sponge P. abyssi, O. Schmidt , and the fossil , P. primoei'a, 

 Zittel. It is true that in both the recent and fossil Pacha- 

 strellid sponges, various forms and sizes of quadrifid spicules 

 are present in the same sponge, but as I have not noticed 

 any sponges with spicules having the short, blunted arms of 

 these examples, I think they may belong to a distinct species, 

 which I propose to name in honour of Mr. H. J. Carter F. R. S. 



Pachastrella primaeva ? 



Zittel: Stud, iiber Foss. Spongien p. 100, Taf. XII, fig. 4. 



(Plate III, figs. 28, 32, 33, 34). 



Spicules with four unequal arms , ' straight or slightly 



