R. M. Brydone — New Cretaceous Polyzoa. 3 



wide, and even triangular radiating slits; aperture horseslioe-shaped, 

 posterior lip formed by the broad unthickened slightly upturned 

 margin of the front wall, and uniting with the anterior lip to form 

 a thin subtubular peristome. 



Ooscia occurring freely but very erratically, relatively small, with 

 rather narrow apertures cut slightly back. 



Avicularia. — {a) Vicarious, average length '6 mm., with beaks of 

 the hour-glass type, but scoop-shaped, with almost parallel side 

 walls hardly folded over or constricted at all in the middle or 

 expanded at the ends ; the posterior end of the beak is tilted up on 

 a strongly inflated external wall; the aperture is long and narrow 

 with rounded ends, the posterior end being bluntly rounded and 

 enclosed by a very narrow internal front wall, and the anterior end 

 tapering somewhat and being enclosed by a wide internal front wall. 

 (J)) Accessory, small roundish lumps with arrowhead - shaped 

 apertures standing up high and possibly sometimes supported on 

 slender legs like those of 3£. Sherhorni, Bryd.'; very abundant, 

 grouped thickly round the apertures, sometimes as many as four to 

 an aperture, but very rare away from tlie apertures. The vicarious 

 avicularia are very erratic in occurrence, and do not seem to appear 

 until the zoarium has reached a fair age, so that they can only be 

 expected at the edges, if at all, in small or medium-sized zoaria. 



This species seems to be coeval with 31. manonia^ Eryd.,^ and like 

 it very characteristic of and restricted to the lower part of the zone 

 of B. mucronata in Hants and the Isle of Wight. ^ It has been found 

 at the very base of that zone at Bedhampton, Hants, but never yet in 

 tlie zone of A. quadratus. It forms a very natural introduction to 



Membraniporella. Trimensis, sp. nov. (PI. I, Figs. 8-10.) 



Zoarium unilaminate, adlierent or free. 



Zocecia large, average length -9 to -95 mm., distinct, decidedly 

 pyriporiform ; front walls arched, arising at an angle from the edges 

 of the side walls, and pierced by about four pairs of short, broad, 

 and sometimes triangular slits, with a broad band separating the 

 uppermost pair of slits from the aperture and merging at its ends 

 imperceptibly into the side walls ; aperture typically about five- 

 eighths of a circle, with a short, straight, posterior lip, but rather 

 variable in shape ; posterior lip short and straight with a slightly 

 upturned edge, which sometimes develops into a median denticle, 

 and combines with the anterior lip produced upwards and slightly 



^ Ibid., 1906, pp. 289-300, Fig. 7 (as Cribrilina Slierborni). 



2 Ante, p. 146. 



^ There is a very similar form in the Weybourne Chalk, in which according 

 to my only good specimen the front wall has the slits usually obliterated by 

 calcification, the aperture is vei-y irregular in shape and sometimes sharply 

 triangular owing to the encroachment of the accessory avicularia, the 

 accessory avicularia are only slightly prominent, and the vicarious avicularia 

 are longer and wider and expanded at the anterior end, being of the same 

 general outline as those of Memhranipora invigilata, Bryd. (Geol. Mag., 

 1910, p. 76), and the remains of the transverse bar are much more pronounced. 

 I should not care to commit myself to its being a distinct species on practically 

 one specimen, but if so it might be named M. Weyiournensis . 



