FRESH WATER SPONGES OF NOVA SCOTIA—MACKAY. 237 
3. S. Mackayi, Carter. 
Sessile, encrusting, with many large compound statoblasts 
prominent through the thin layer of flesh. Large gemmules 
» inch in diameter consisting of about 16 statoblasts, apertures 
turned inward, supported by a mass of heavily spined acerate 
spicules of various sizes, intercrossing. Spines sometimes as 
long as the spicule is broad, very irregular in size and situation, 
skeletal spicules longer and all parts more slender. Described 
by Carter, in the “Annals and Magazine of Natural History.” 
London, January, 1885. The species is not uncommon in Nova 
Scotia lakes. Its spicules appear to exist in the diatomaceous 
deposits of the lakes which supply the water system of Halifax ; 
specimens of which we have received from Professor Lawson of 
Daihousie College. Carter has described similar spicules as 
abundant in the diluvial deposits of the Altmiihl Valley in 
Bavaria. (See slides 24 and 25.) It is very near S. igloiformis 
of Potts. 
Genus I].—MEYeEnIa. 
Statoblasts surrounded by minute birotulate spicules. 
4. M. fluviatilis, Carter. 
Massive encrusting, sometimes extensively lobular. Birotulates 
small and star-like, the shaft connecting the rayed discs about 
equal to diameter of rays. 
Varieties of this species (with some adventitious spicules) 
have been described by Dr. G. M. Dawson in the Canadian 
Naturalist of Sept. 1875, as S. stagnalis and S. asper- 
rima. This species, like its old European comrade, S. lacustris, 
is one of our most common sponges. (See slides 26 and 27). 
5. M. Everetti, Mills. 
Sessile, encrusting. Statoblast birotules 3 to 4 times longer 
axially than those of J. fluviatilis, with the more numerous 
rays incurved. Flesh spicules present as minute slender biro- 
tules with incurved barb-like rays. Discovered for the second 
time in the lakes of Pictou County. The only habitat previous- 
