88 A. II. MACKAY ON 



Genus II. — Meybnia. Statoblast spicules, one class of birotulate monaxons, radial. 

 Species 5. — Mcyenia Everetli. Dermal spicules, birotulates. 

 " (). — Mcycnki fluvialilh. 



Genus III. — Heterombyen'ia. Statoblast spicules, two classes of birotulate monaxons, radial. 

 Species 7. — Hctcromcyenia argijrofiperma. 

 " S. — HctfTomcycnia Ryderi. 

 " 9. — Heteromeyenia Ficiovenns. 



Genus IV. — ïubella. Statoblast spicules, ono classe of inerjuibirotulate monaxons, radial. 

 Species 10- — TuhcUa rcnnsylvanica. 



The spiculation of tlie genera and of most of tlie sjiecies is illustrated in the accompanying Plate of eight 

 diagrammatic drawings. A small segment of a statoblast show.s, below, the cellular germinal matter, bounded 

 above by an arc of the enclosing chitinous capsule. The statoblast spicules come next, and when in position 

 are generally embedded in the "crust" which is not sketched, but which immediately invests the chitinous coat. 

 Next above are the skeleton spicules, and above them the dermal spicules when they occur. They are all 

 magnified on the same scale — 200 diameters- 



Synopsis. 



For Ihe sake of brevity, the author here takes the liberty of coudensing or modifying 

 the original descriptions as suggested by his own observations. He feels that many of 

 the synonyms have been based on varietal distinctions ; but he cannot at present attempt 

 the delimitation of Canadian varieties. There are very many species, not to speak of 

 varieties, which are yet to be discovered in this country. With more extensive collections 

 and closer investigation, data for a more complete treatment of our fresh-water sponges 

 may be hoped for in the near future. 



Genus I.— SPONGILLA, Carter. 



Statoblasts more or less spherical ; separate, in dense layers, or aggregated in com- 

 pound, subglobvtlar, minute masses ; invested with siliceous spicules more or less linear, 

 straight or curved, cylindrical or acerate, variously spined, and arranged tangentially to its 

 inner, chitinous, capsular coat. 



A. — Dermal Spicules Absent. 



1.— Spongilla fragilis. 



1851. Spongilla fragilis, Leidy. 



1863. " Lordii, Bowerbank. 



18*70. " contecla, Noll. 



1875. " Ottawaensis, Gr. M. Dawson. 



18*78. " Siberica, Dybowski. 



1880. " Morgiana, Potts. 



1880. " Calumeli, Thomas. 



1880. " fragilis, var. minuta, Potts. 



1880. " " " mimdissima, Potts. 



1880. " " " irregularis, Potts. 



