B. M. Brydone — New Chalk Polyzoa. 437 



shows a very close approach to the early coarse form of C. Gregoryi 

 illustrated by Fig. 3, and makes it important to inquire -what sure 

 distinctions can be drawn between these species. The most prominent 

 feature of C. suffulta is the arched front wall with depressed central 

 area — it does not show up well under the microscope but is very 

 striking under a pocket lens — but this feature is occasionally very 

 closely imitated, owing no doubt to local conditions, in an otherwise 

 typical zoarium of C. Gregoryi. But the slits in the front wall, 

 which in C. suffulta replace pores in C. Gregoryi, and the stout paired 

 tubercles at the upper end of the aperture of C. Gregoryi, seem to be 

 absolutely reliable distinctions. 



Cribbilina Cacus,' sp. nov. (PI. XIV, Figs. 6-8.) 



Zoarium unilaminate, always encrusting. 



Zooscia subpyriform and very large for this genus, such measure- 

 ments as l"2mm. for length and •9 mm. for breadth being quite 

 usual ; side walls quite distinct ; front walls lying on the side walls, 

 flatly convex, pierced by from twenty to twenty-six rows of pores 

 more or less opposed in pairs, the pores tending to increase markedly 

 in size at the outer ends of the rows ; aperture definitely but not 

 strongly horseshoe-shaped and bearing on its rim four or five more or 

 less perforated tubercles, the lower pair much stouter and less deeply 

 perforated than the upper ones, while when three upper ones are 

 present the middle one of them tends to be distinctly more slender 

 than the others. 



Ooecia quite scarce and very brittle, the one figured (Fig. 8) being 

 the only perfect one I have yet seen : it was very large and globular 

 with a tendency to a bottle neck, and two stay-like rods running 

 obliquely upwards to it from the sides of the aperture; unfortunately 

 it was destroyed by an accident after it had been photographed. 



Avicularia perhaps represented by shallow, slightly _ ear-shaped 

 rings sparingly tucked away among the zocecia, resembling those more 

 freely found in Cribrilina Bihleyi, mihi? 



This species, which occurs from time to time at Trimingham, might 

 almost be regarded as a double scale variety of C. Bihleyi, a figure of 

 which is given for comparison. At the same time, this giant form 

 occurs often enough to indicate the existence of a definite race ; and 

 as there are no intermediate forms, and the difference in size is so 

 considerable, I have thought it justifiable to constitute it a separate 

 species. Support may be found for this view in the differing shapes 

 of the respective apertures and the total absence from C. Cacus of 

 anything to correspond with the graceful and abundant avicularia of 

 C. Bihleyi. Crihrilina Guascoi, Ubaghs, sp. {Eseharipora Guascoi, 

 Ubaghs, Verh. d. Nat. Ver. Preussen Itheinh, Jahrg. xxii, p. 51, 

 taf. ii, fig. 3), seems a close parallel in size and general type. 

 Membeaniporella Shekboeni, mihi sp. (PI. XIY, Fig. 10.) 



Syn. Crihrilina Sherhorni, mihi.^ 



Further investigation has shown that the radiating ribs of the front 

 wall are not united to one another in any way, and the species must 



^ Cacus, a giant in Latin mythology. 

 2 Geol. Mag., 1906, pp. 289-300. 



