226 DR. nmDE and mr. holmes on sponge-remains 

 Group Clayulina, Vosmaer. 



Family Spirastkellid^, Bidley Sf Dendy. 



No. of Flesh- Skeleton- 



Species. G-enus. Spicules. Spicules. 



2 Splrastrella, Osc. Schmidt . . .' E.S. & S.S. 



2 Pronax, Gray F.S. & S.S. 



Family LATRUKCULiDiE, nov. 



15 Latrunculia, Socage F.S. & S.S. 



2 Thoosa, Hancock F.S. & S.S. 



1 Alectona, Carter F.S. & S.S. 



70 



In this list 24 genera are enumerated and 70 species. Four 

 genera are considered doubtful, and no species are placed under 

 them, since they are only represented by skeleton-spicules. Of 

 the other genera, distinctive flesh-spicules have been recognized 

 in all, with the exception of" Plocamia, Osc. Sch., and in this 

 genus the dumb-bell forms of skeleton-spicules are sufficiently 

 characteristic. In estimating the number of species we have 

 taken into consideration the fact that in recent sponges of this 

 group there are many characterized by only a single distinctive 

 form of flesb- spicule, whilst in others there are two or occa- 

 sionally three distinctive forms. 



It will be seen that the genera most numerously represented 

 are Esperella with 10 species, Desmacidon and Myxilla with 12 

 species between them, and LatruncuUa with 15 species. "We 

 venture to consider this latter genus as the type of a new family, 

 distinguished by sceptrelliform flesh-spicules. Hitherto, the 

 genus has been placed in the Bpirastrellidce by E,idley and 

 Dendy, but there does not appear to be any form-relationship 

 between the spiral flesh-spicules of this last-named family and 

 the sceptrellas of LatruncuUa and its allied genera Thoosa and 

 Alectona. By Yosmaer LatruncuUa, or its synonym Sceptrella^ 

 was placed in the DesmacidonidcB on the supposition that it 

 possessed an anchorate flesh-spicule, but, as already mentioned, 

 this anchorate is in all probability adventitious. 



The significance of so many species of Monactinellid sponges 

 from this single fossil deposit will appear the greater from the 

 fact that the ' Challenger ' Expedition only obtained 16 recent 



