new Recent Pharetronid 8j_)onges. 505 



The oscular surface is covered with numerous oscular bee- 

 hive-shaped or cylindrical chimneys, with a very contracted^ 

 orifice at the summit; the height is about 2 mm. Only a 

 few remain intact, most having been knocked off or squashed 

 inside the hard cylindrical bases, which rise up about "5 mm. 

 above the surface ; the youngest oscules at the periphery lie 

 al-ong the course of grooves and are flush with the surface. 



The smaller specimen (B) is in the form of an ear-shaped 

 lamella with the poral surface on the concave side ; the 

 breadth is 3'5 cm., the height 3 cm., and thickness 5 mm, 



The poral surface is covered with a soft, fleshy, ectosomal, 

 nmber-coloured layer, whence the low densely crowded pore- 

 chimneys arise ; the oscular surface is lighter in colour, and 

 the ectosome is barely discernible excepting along certain 

 peripheral grooves. 



The outward appearance of Minchinella closely resembles 

 that of species of the fossil Pharetronid genus Rhaphidonema 

 Hinde (2. p. 97). 



The fractured surface of the sponge is of a pale cream- 

 colour, and, excepting for the larger incurrent and excurrent 

 canals, homogeneous in aspect. Under a lens a fine reticulum 

 can be made out ; in a transparent vertical section the net- 

 work is seen to be denser externally than at tlie centre. 



The Canal System. — The canal system is well shown in 

 stained vertical sections of decalcified sponge, and also by 

 tracing out with a needle the course of the larger incurrent 

 canals seen on the broken surface of a dried macerated 

 fragment. 



The oscules open below into wide excurrent canals, which 

 give off a series of smaller canals ; the latter, by branching 

 and anastomosis, form a tubular network, often with quite 

 regular rectangular meshes and with terminal blind branches. 

 The tabular strands, but more especially the nodes, are beset 

 with spheroidal flagellated chambers 32'5 fx, in diameter. 

 The breadth of the strands averages about 40 /i, and of the 

 nodes 52 jx, but the soft tissues have been much contracted in 

 preparation. 



The collar cells are large, with a flattened body containing 

 a very large nucleus nearly filling the cell. 



Viewed in optical vertical section, the body of the cell is 

 low, mound-shaped, resembling in this aspect Hexactinellid 

 collar cells figured by Ijima (3 a. pi. v. figs. 40, 41) ; the base 

 has a circular outline and the nucleus is always seen at the 

 side of the cell. The collar forms a long slender funnel 

 arising from a point situated a little excentrically. The 

 flagellum is clearly visible outside the collar, but I could not 

 trace it down inside. Prof. Minchin, to whom I showed the 



