Polyzoa, Ccelenterata, and Sponges. 451 



such a space. At the opposite side of the colony the cells are 

 flattish, Avith a central rather minutely tuberculated area ; the 

 sides of the cells are formed by smooth spaces containing a 

 few coarse perforations ; there is a slight approach to a rostrum 

 immediately below the mouth. This form is well represented 

 by the two left-hand cells of Busk's pi. xcix. fig. 4. A broad 

 rounded denticle lies within the mouth in all these forms ; the 

 ooecium is globose, tuberculate, slightly prominent. 



Hab. On large univalve shells. 



The numerous variations exliibited by this species are, as 

 Hincks remarks {he. cit. p. 324), mainly due to superficial 

 differences ; the form of the mouth, the denticle (except in the 

 doubtful specimen, in which it is rectangular), the infraoral 

 avicularian rostrum (or the depressed space representing it), 

 the marginal punctures maintain the same general characters 

 throughout. No spines, or traces of them, however, were ob- 

 served in any cells ; but as Hincks only figures them in one 

 case and Busk not at all, they must be regarded as very rarely 

 occurring. 



The possibility of tlie presence or absence of avicularia in 

 different specimens of the same Polyzoau species would be 

 a striking fact if it were determined to be a real possibility ; it 

 would, however, be interesting to determine whether, as in 

 this case, the absent avicularium is not generally represented 

 by the rudiments of a chamber in the surface on which it 

 should normally occur. Occlusion of the avicularium by 

 thickening of the cell-wall must also be allowed for when 

 it is stated to be absent in any given species. 



Mucronella ventricosa^ Hassall, var. connectens. n. var. 

 (PI. XXI. fig. 6.) 



Discopora coccinea, forma ventricosa, Smitt ?, pars, (Efy. Akad. Forh. 

 1867, Bihang, p. 172, pi. xxvii. fig. 167 only. 



A small colony without ooecia, unless the remarkable pro- 

 minence figured in fig. 6 & is an abnormal ooecial hood. It 

 agrees neither with M. FeacMi^ Johnst., nor with M. ventricosa^ 

 but has several points which appear to connect the two species. 

 The cells are large, glistening, and convex, marked with radi- 

 ating tuberculated lines and a marginal row of perforations ; 

 they are arranged in regularly radiating series, separated by 

 deep furrows. The mouth is constant in the possession of six 

 spines; the denticle is broad, with more or less prominent lateral 

 points, and is well represented by those given in Smitt's 

 figure cited above. There is a considerable space, contain- 

 ing variously shaped fenestroe, in continuation with the mar- 



