24 



of the sponge remains, and at first led me to doubt whether 

 they were spicules, but the presence of the interior canal 

 points them out to be such. With one exception, in which 

 there is a slight tapering at one extremity, all these spicules 

 terminate abruptly, as if broken off at their ends, and therefore 

 may be regarded as incomplete. One of the longest of these 

 fragmentary spicules is 5,175 mm. long by 0,225 mm. wide, 

 others are only 0,135 mm. in width, but their outer surfaces 

 are so eroded that originally they may have been considerably 

 thicker. It is quite a matter of conjucture as to the sponge 

 of which these were the skeleton spicules, as, so far as I am 

 aware, no sponge with similar spicules has yet been described. 

 In Scolioraphis anastomans Zittel (Studien liber foss. Spong. 

 p. 95, Taf. XII, fig. i) there are also sinuous spicules, but 

 they are provided with knobbed surfaces, and are much smaller 

 than these from Horstead. 



Order Tetractinellidae, Marshall. 



The characteristic spicule of this division of sponges has 

 four arms or rays, one usually much longer than the others, 

 radiating from a centre. Each ray is provided with an in- 

 terior canal which unites with those of the other rays and, 

 where the rays are bifurcated, the canal is also bifurcated and 

 a branch extends into each division. There are two principal 

 forms in which these quadriaxial spicules may be divided. In 

 one there is a great development of a single ray, which be- 

 comes an elongated gradually tapering shaft, pointed at one 

 end, whilst from the other and usually the thickest portion of 

 the shaft, there spring three short arms or rays in very va- 

 rying directions ; in some spicules prolonged backwards , fork 

 like, nearly in a line with the shaft itself; in others, at varying 

 angles between the perpendicular and horizontal ; whilst in other 

 spicules the rays curve backwards , in the direction of the 

 point of the shaft, and become anchor-shaped. These three 



