R. M. Br //done— On Chalk Bryozoa {Pohjzoa). 399 



Cribrilina ostreicola, nov. PL XXIII, Figs. 1 and 2. 



Zoarium always encrusting. 



Zooecia pyriform, average length and breadth •45 mm. and •28 mm.; 

 aperture semicircular, lower lip often curved slightly outwards ; front 

 wall composed of from 13 to 15 spines more or less arranged in 

 opposing pairs and separated by furrows with a large pore at the outer 

 end and otherwise finely punctate. 



Oaciwn large, globose, the free edge corresponding in outline with 

 but slightly smaller than the upper lip of the aperture. 



Avicularia very numerous and of three classes, all of duller texture 

 than the zooecia. The most abundant are small and slender, with 

 a strong inflation of the upper end, in which a slit-like aperture is 

 set, and lie in almost continuous lines between the lines of zooecia. 

 The second class are mandibular, of regular occurrence, and often 

 vicarious, with a central oval aperture surrounded by a slender ring, 

 and a rounded symmetrical beak. The third class (possibly vibracularia) 

 occur ver}' irregularly and are large and quadrangular, with a 

 relatively verj' small oval aperture rather above the centre. 



Veiy abundant at Trimmiugham, mainly on Ostrece. 



Cribeilina subviteea, nov. PI. XXIII, Figs. 3 and 4. 



Zoarium always encrusting. 



Zooecia small, average length and breadth "45 mm. and "28 mm. ; 

 aperture transversely oval, with a deep subtriangular slit in the lower 

 lip ; front wall tumid, with many imperforate radiating furrows too 

 faint to be accurately counted. 



Ooecia tumid, elongated, subtriangular, very faintly keeled and 

 transversely farrowed, free edge corresponding in outline with but 

 smaller than the upper lip of the aperture. 



Avicularia of two classes. The first class small, narrow, pointed, 

 with oval apertures, usually in pairs like horns at the head of the 

 zooecium, \evy constant. The second class (possibly vibracularia) are 

 vicarious, polygonal, with verj- small central circular apertures, 

 occurring irregularly and often in bands and groups. 



These vicarious avicularia and some of the zooecia are depressed 

 below the general surface, and have a dull appearance like that of 

 roughened glass. The dull zooecia show the radiating furrows much 

 better than the normal ones. 



This species is very closely related to the form identified by 

 Beissel' Avith Cellepora elegantula. Hag., undoubtedly in error, but is 

 easily distinguishable by its imperforate surface and vicarious 

 avicularia. Marsson ' has referred Beissel's form to Schizoporella 

 cornuta, Hag. sp., but it is clearly a strict Grihrilina, and being 

 unnamed may be called Crihrilina Beisseli. C. siihvitrea is technically 

 a Schizoporella, but its close relationship to C. Beisseli makes me feel 

 justified in regarding its furrows as genetic and classifying it as 

 a Crihrilina until the time comes for the Cribrilinidae to be dis- 

 membered. 



Abundant at Trimmingham. 



1 iiber die Brijozoen der Aachner Kreidehildiing, Haarlem, 1865, p. 60. 

 * Op. cit. 



