52 R. M. Bvydone—New Chalk Polyzou. 



Aoieularia tiny hoods with circular apertures placed immediately 

 above the zocecia in the middle Hue with great regularity when no 

 ocecium occurs ; when there is an ocecium the avicularium is 

 suppressed or, very occasionally, displaced to one side ; one or two 

 instances in which they appear to have no aperture are probably due 

 to the aperture being blocked by "a fragment of shell. 



This species is rare in the If. cor-testudinarium zone at Seaford. 

 Lt illustrates well the building up of the Cribrilinid front wall from 

 marginal spines, the bases of the spines being still distinguishable. 

 It is probably ancestral to Cribrilina cieatrieifera, Bryd. 1 



Since the above paper was framed I have seen Mr. Lang's Revision 

 of the " Cribrimorph" (i.e. Cribrilinid) Cretaceous Polyzoa in Annals 

 and Magazine of Natural History for July and November, 1916. I am 

 glad to find that he adopts the view I propounded in 1906 (Geol. 

 Mag., July, 1906, p. 289) that the characters by which the genera 

 Cribrilina and Membraniporella are distinguished are not of generic 

 nature. In replacing this principle of classification he has created over 

 fifty new genera. It would obviously be a considerable task, for which 

 I neither have time nor claim authority, to sit in judgment on such 

 a volume of new material, particularly as it is not accompanied by 

 a single illustration, and many of the new genera do not rest on any 

 species figured elsewhere. It is fairly open to doubt whether as 

 a rule any verbal description of characters among forms so small, 

 numerous, and complex as the Polyzoa can be relied on as adequate 

 definition of a new genus. The same consideration applies with even 

 greater force to the very great number of new species which he 

 catalogues without figuring any of them. It is not too much to say 

 that the most detailed diagnosis without reference to a figure is now 

 insufficient to identify any form among the vast crowd that either 

 have already been adequately described or still remain to be so 

 described. Mr. Lang's catalogues certainly do not amount even to 

 detailed diagnosis, and it is impossible to treat his new species as 

 identified sufficiently to be accepted as validly established. When 

 they have been figured they will be sufficiently definite for useful 

 study ; but a cursory inspection of the catalogues suggests that some 

 of them may have a hard struggle for existence unless the points 

 which appear in the tabular diagnoses are substantially supplemented. 

 It gives, for instance, a very retrograde impression to find unilaminar 

 forms of Cribrilina Gregoryi divided solely by whether they grew 

 incrusting an imperishable object or are now found free into two 

 species (perhaps to be increased to three on Mr. Lang observing that 

 though the majority of the free forms have a prickly reverse side 

 a substantial minority are smooth). I shall also be much surprised if 

 there should prove to be a bilaminar race of Cribrilina Gregoryi, that 

 is, something more than an isolated freak or a unilaminar zoarium 

 which has happened to incrust rather neatly the reverse side of a free 

 unilaminar zoarium, at the horizon with which of all Chalk horizons 

 I am perhaps most familiar. 



1 Geol. Mao., 1914, p. 97, PI. IV, Figs. 1, 2. 



