[lambb] sponges from THE ATLANTIC COAST OF CANADA 193 



.slightly beyond the surftice. The larger tylostyli form an inner cortical 

 layer and are loosely and irregularly dispose<l. The dense outer portion 

 occupies scarcely one-third of the entire thickness of the cortex. Pro- 

 jecting beyond the general surface and with theii- bases embedded in the 

 cortex are tylostyli similar in form to those of the main tibres but much 

 longer. At the margin of the osculum the })r<)jecting tylostyli are 

 directed towai'd a point a little above the centre of the opening. 



Spicules. — (a) Megasclera ; (1) stout, fusiform, gradually and 

 sharply pointed t3dostyli, with rather feebly developed heads; forming 

 the skeleton fibres (Plate 11., tig. 5a) ; length from 0959 to 1-78 mm., 

 with an average thickness of 0-027 mm. (Bowerbank"s xheleton spicula). 

 (2) Small, sharply pointed often slightly bent tylostyli varying consider- 

 ably in thiclvness and generally with well developed heads ; contined to 

 the dermal layer of the cortex (Plate II., fig. 56) ; length from 0-091 to 

 0-189 mm., thickness from 0-002 to 0-004 mm. (Bowerbank's secondary 

 series of defensive spicula). (3) Stout, sharply pointed, slightly bent tylo- 

 styli, with well marked heads (Plate II., fig. 5f) ; forming the inner layer 

 of the cortex ; they var3^ in length from 0-232 to 0-575 mm. and in thick- 

 ness from 0-006 to 0-013 mm. (Bowerbank's feri.-<ion spicula). (-l) Long, 

 slender, sharply pointed tylostyli, with heads slightly more marked than 

 those of the tylostyli of the skeleton fibres ; projecting far beyond the 

 general surface (Plate IL, fig. 5d) ; maximum length 3'(j mm., maximum 

 thickness 0-02 mm. (Bowcrhank' s primary series of defensive spicula). 



Localities. — Portland, Maine, one specimen, dry and one in alcohol. 

 Sir \Yilliam Dawson ; dredge J, twenty-four miles south b}' west of East 

 Point, Anticosti, in 212 fathoms, mud and stones, temperature of mud 40° 

 Fahr., one specimen, preserved in alcohol. J. y. Whiteaves. 1871. 



Distribution. — IS'ortheast coast of United States (Sir William Daw- 

 son, Verrill) ; Gulf of St. Lawi'ence (J. F. Whiteaves). 



Polymastia robusta, Bowei-bank. 



(Plate IL, figs. 6, Qa. 66.) 



Euplectella robusta, Bowerbank. IS60. List of British Mcarine Invertebrate Fauna, 



Rep. of Brit. Ass., p. 236. 

 Polymastia robusta, Bowerbank. 1866. Mon. Brit. Spong., vol. ii, p. 62, vol. iii., 



p. 23, pi. X., figs. 5-8, and vol. iv., p. 31. 

 Polymastia robusta? Verrill. 1874. Am. Jour. Sci. and Arts, vol. vii., p. 4-1. 



" " Ridley and Bendy. 1887. Rep. Monaxonida, Zool. Chall. Exp. 



vol. XX., p. 210, pi. xli., fig. 8. 



A number of specimens of this sponge in a good state of preservation. 

 The one figured (Plate IL, fig. 6) is 52 mm. long., 42 mm. broad and 

 about 4 mm. thick. On its upper surface are fifteen fistula^ having a 

 maximum diameter of 3 mm. at the base and not exceeding 25 mm. in 

 length. Another specimen has twenty-eight fistuhv, having an averai^e 



