390 Mr. W. J. Sollas on the Flint 



Choristidae. 

 Pachastrellites fusifer. (PI. XX. fig. 28.) 



This fusiform acerate, with its ovate swelling in the middle, 

 resembles the spicule figured by Schmidt (Taf. vi. fig. 5, 

 Atlant. Spong.) from Pachastrella connectens. 



A similar form occurs in Papyrula Candida, 0. S., and in 

 some Hexactinellids. That it did not belong to a Hexacti- 

 nellid appears to be shown by the fact that the canal, which 

 frequently occurs in a much enlarged state, never presents a 

 sexradiate cross within the central bulb. It is true that this 

 test is not quite so decisive as one could wish, especially as 

 the canal is altered by enlargement, expanding within the 

 bulb concentric with its surface. On the whole, however, 

 it appears probable that this spicule should be placed with the 

 Pachastrellidoe ; and we may provisionally associate with it the 

 trifid spicule (fig. 29), and perhaps the bent acerate (fig. 38). 



Pachastrellites globiger. (PI. XX. fig. 39.) 



Fig. 39 is a tubercular globate spicule very similar to that 

 figured by Carter as occurring in his P. geodoides (' Annals,' 

 ser. 4, vol. xviii. pi. xiv. fig. 23). 



Fig. 40 is similar, but differs in the somewhat more regular 

 size and disposition of its tubercles. They may have been 

 associated with the form fig. 30, and perhaps with spicules 

 like figs. 29 and 38 as well. 



T thylites cretaceus. (PI. XX. figs. 31, 32.) 



Wright, Irish Cret. Microzoa, he. cit. sphserostellate spicule. 



These two spicules are undistinguishable from the stellates 

 of Tethya lyncurium ; and figs. 33 and 51 represent acuate 

 spicules like those of T. lyncurium. Zittel has already given 

 the name Tethyopsis to a form which he considers related to 

 Tetilla, Sdt. As it appears to me that Donatia cannot be 

 allowed to replace Tethya in our nomenclature, I cannot call 

 my form Donatites, and so form its generic name from Tethya 

 with the termination " lites." 



Triphyttactis elegans. (PI. XX. fig. 42.) 



This trifid spicule with broad trifurcate arms, inclined from 

 the shaft as much upwards as outwards, vasiform, is unlike 

 any known recent or fossil form. It varies from ^ott to y^ inch 

 in the length of its rays. Schmidt has lately figured (Spong. d. 

 Meerbusen v. Mexico, 1880, Taf. ix. fig. 4) some spicules 

 which agree in the essential character of having trifid arms ; 



