70 

 Stauractinella cretacea, n. sp. 



(Plate V, figs. 9, 10, loa, n). 



Large free hexactinellid spicules, arms mostly straight, 

 nearly of an equal thickness throughout or very gradually 

 tapering , one axis frequently much longer than the others ; 

 the central node solid and but slightly , if at all , inflated. 

 Extreme length of spicular arms 2,18 mm. ; thickness 0,1 12 mm. 

 Abundant. 



Spicules with the above characters are numerous in the 

 Horstead flint and from their dimensions and isolated condition 

 appear to belong to the sub- order Lyssakina. In one in- 

 stance however, I have met with an example (fig. 9) in which 

 two spicules are apparently connected, but as the arms of 

 one are very short , it may be merely a case of abnormal 

 growth. The majority of these spicules have one axis much 

 longer than the others, but in none of the examples are the 

 extremities of the spicular arms complete, and it is quite pos- 

 sible that they may have extended in an attenuated form to a 

 considerable length, and would have then presented a greater 

 resemblance to the spicules of the existing sponges of this 

 sub - order. One spicule (fig. 10 a) differs from the rest in 

 having one arm truncated and rounded a short distance from 

 the node, and the other arms are thinner and pointed. The 

 interior canals of these spicules are but rarely preserved, 

 when present they are of an abnormal width. 



The relationship of these free hexactinellid spicules ap- 

 pears to be very near to Stauractinella jurassica, Zittel 

 (Studien iiber fossile Spong. p. 60) in which similarly shaped, 

 but much larger spicules than these from the Chalk Strata, 

 form the skeletons of large spheroidal sponges. As they are 

 readily distinguished from the Jurassic forms , I propose to 

 name the sponge to which they belonged Stauractinella cre- 

 tacea. A similar spicule, but so far as I can judge, of much 

 smaller size has been found in the Chalk of the North of 

 Ireland (Wright: op. cit. PI. Ill, fig. 4). 



