94 A. H. MACKAY ON 



8. — Heteromeyenia Ryderi. 



1882. Heleromeyenia Ryderi, Potts. 

 1885. " " MacKay. 



Sponge greenish, in massive encrustations, texture loose, svirface more or less lobed. 

 Skeleton spiciiles non-fasciculate, nearly 0.013 by O.OOOG iucli, fusiform, spiued except at 

 the extremities. Statoblasts Avith iucouspieuous tubular foramina. Greater birotulates, 

 about 0.0023 by 0.00025 inch ; diameter of rotules 0.000(3 inch. Shafts with spines hooked 

 towards their centers. Rotiiles of three to six short recurved hooks. Leaser birotulates, 

 0.0012 inch long. Diameter of rotules 0.0009. Shafts sometimes spined, enlarging 

 towards the rotules which are flat disks with laciuate margins. 



Habitat. — Lakelets and old millpond, Pictou Co., Nova Scotia. — MacKaij. 



9. — Heteromeyenia Pictovensis. 



1885. Heteromeyenia Pictovensis. Potts. 



1885. " " MacKay. 



1887. " Ryderi, A'ar. Pictovensis, Potts. 



Sponge green, massive, encrusting. Texture very compact. Surface smooth. 

 Spicules non- fasciculated, 0.00*75 by 0.000*75 inch. Short, robust, cylindrical, curved, with 

 spines diverted towards the ends which may ])e round and spined or sharply conical. 

 Statoblasts scarce. Greater birotulates, about 0.0021 inch with fusiform shafts often spined 

 near the middle, and rotules of three to six irregularly placed rays recurved at their 

 extremities. Lesser birotulates, about 0.0012 inch. Diameter of the disk-shai^ed rotules 

 0.0009 inch, umbonate, with lacinulate margins. 



iïa6/ia<.— Lakelets in Pictou Cou.nty drained to the Atlantic by St. Mary's River, 

 On stones in a small stream flowing into the North-West Arm, Halifax. Spicules of, in 

 sediment of Dartmoiith lakes, etc., all in Nova Scotia. In lakes between Conception 

 Bay and Trinity Bay, and at Harbor Grace Junction, in Newfoundland. 



This is the firmest and most beautiful of our iresli- water sponges. So distinctive is 

 this character that it can generally be recognised at sight. Although its texture and 

 statoblast spiculation bear a degree of resemblance to those of H. Ryderi, the skeleton 

 spicules are so different from those of that species, its varieties, and all other known fresh- 

 water sponges, that it appears to have a clear claim to specific rank. The statoblast 

 spiculation has very judiciously been taken as an artificial criterion for generic delimita- 

 tion. But to make its morphology the chief factor in specific grouping, against so 

 thoroughly distinctiA'e a skeleton spiculation, looks like forsaking the phylogenetic idea 

 of classification for an artificial one which has no practical advantage. The palaeontolo- 

 gist finding these sponge spicules in his geological formations would be likely to go to 

 the other extreme, and make //. Pictovensis generically distinct from H. Ryderi. 



