FEESH-WATEE SPONGES. 9S 



Genus IV.— TUBELLA, Carter. 



Granular crust of statoblasts charged with trumpet-shaped, or iuequibirotulate 

 spicules, the larger rotule resting upon the chitiuous cai^sule. 



10. — TuBELLA PeNNSYLVANICA. 



1882. Tubella Pennsylvanica, Totts. 

 1885. " " MacKay. 



1887. " ". Potts. 



Sponge minute, incrusting, greenish when growing in the light. Surface of mature 

 specimens often found bearing i^arallel skeleton spicules not arranged to form cell-like 

 interspaces. Skeleton spicules variable as to length and curvature, averaging 0.0066 by 

 0.0003 inch, subfusiform, acuminate or rounded, entirely spined ; spines large, conical ; 

 terminations of spicrrles more often round than acuminate. No dermal sf)icules. Stato- 

 blasts small. The diameter of the distal rotule may vary from that of the shaft to that 

 of the large rotule. Margin of large rotule generally entire. Dimensions of inequi- 

 birotulates 0.00035 by 0.0001 inch. Diameters of rotules 0.0007 and 0.00015 inch. 



Habitai.— Oil stones in margin of Quidi Yidi Pond, St. John's, Newfoundland, and in 

 lakelets, Pictou County, Nova Scotia. — MacKay. 



The rotules of the Newfoundland species differ from the Nova Scotian by having the 

 rotules of the statoblast spicules distinctly crenate-rayed. 



