PoJyzoa of the St. Lawrence. 223 



masked by the great extension of the avicularian chamber, 

 which ultimately covers a large proportion of the front of the 

 zocecium. Before its appearance the latter is very mode- 

 rately convex, the peristome not elevated, the surface smooth, 

 the orifice arched above and slightly curved below. In most of 

 the marginal cells the avicularium is already outlined. At the 

 top it is of equal width with the orifice ; from this point it 

 tapers oif for a short distance, and then continues subtubular 

 to the base (PI. XV. fig. 5 a). When it is fully developed 

 and enlarged by the progress of calcification the zooeciiim 

 appears cylindrical. In later stages, when there has been a 

 large accretion of calcareous matter, the divisions between the 

 cells become inconspicuous, the surface is nearly level and 

 uniformly granular, and the avicularium, so prominent at 

 first, is deeply sunk in the shaft-like cavity of the orifice. In 

 the lower portion of the zoarium and for a considerable dis- 

 tance above the base the cells are almost wholly obliterated, 

 and the surface is smooth and glossy. 



Concurrently with the growth of the avicularium the peri- 

 stome rises and the secondary orifice is formed. If the 

 " pouch-like " avicularium is not a generic distinction (and 

 the course of its development agrees very closely with that of 

 the corresponding structure in Porella) there is nothing to 

 separate this form from the last-named genus. 



The variety {rostrata) in which the anterior portion of the 

 avicularium is free and rises into a prominent rostrum over- 

 hanging the orifice (PI. XV. fig. 5) occurs in the St. Law- 

 rence. The species seems to be common in this region, and, 

 so far as we know, is confined to. the northern and arctic 

 seas. It forms light and very elegant coral-like growths, 

 which originate in a small spreading base, on stones &c., 

 much branched, the main branches somewhat antler-shaped, 

 springing from a little above the point of attachment, divided 

 and subdivided into numerous branchlets, which terminate 

 above in more or less expanded subtruncate segments. 



Range. Newfoundland, Labrador, Finmark, Greenland, 

 Spitzbergen, Barents Sea, Kara Sea, ofl:' Hare Island, Baffin's 

 Bay, Nova Zembla. 



Canadian Postpliocene {Sir J. W. Dawson). 



Porella 'prohoscidea^ n. sp. (PI. XIV. figs. 4.) 



P —Bsehara verrucosa, Smitt, form 2, Kritisk Forteckn. 1868, p. 142, 



pi. xxvi. tig. 135. 

 Eschara cervicornis, forma verrucosa, Bryozoa from Nova Zembla 



(Efversigt af Kongl. Vetensk.-Ak. Forliaudl. 1878, no. 3 ; Receusio 



animal. Bryozoorum qua; ad peninsulam Kola invenit F. Trybom, 



ibid. 1878, no. 7. 



