I 



THE RED CHALK OF HUNSTANTON. 4.')7 



Polyzoa ' his family-arrangement of the Cyclostomata has been 

 accepted,, either intact or modified in the smaller divisions, by 

 competent authorities working on fossil groups more especially. 

 Thus, Dr. Pergens, while Avorking along the lines of Hincks, 

 generally adds to or modifies the family-arrangement according 

 to circumstances ; so also Mr. Waters, working along the same 

 lines, suggestively leaving out the family grouping, arranges genera 

 only, and formulates two convenient sections, in either of which 

 fossil and recent Cyclostomata can be appropriately placed. The 

 family-arrangement of the Cyclostomata, as adopted by Dr. ^Lars- 

 son *, is both novel and peculiar, but cannot be dealt with so 

 fully as I could wish in the present memoir. The author established 

 two divisional types to include the Iliigen species of Cretaceous 

 Polyzoa : — I. The Solenoporina, Marsson, embracing six well- 

 known Pamily-groups ; and II. The Metoportna, Marsson. in 

 which he places, in the Family Ceidea, the genus Filicea, d'Orb., 

 and in the Family Eletdea the heretofore much misunderstood 

 genera, Afelicertites, Homer, and Nodelea, d'Orb. 



I am aware of the nomenclatural difficulties which Mr. E. A. 

 Walford had to encounter in his Liassic paper (r)ibliograph. 29), and 

 also in his more recent memoir on the " Inferior-Oolite Bryczoa" 

 (Bibliograph. 30). It is not only difficult, but almost impossible to 

 arrange fossil Polyzoa occurring in and below the Chalk under the 

 modern family-grouping. The Tubuliporidic of Hincks include Sto- 

 matopora, TvhvUjHyra, Idmonea, Entalophora^ and Dtastopora. In 

 one sense certainly this grouping is convenient, but the difficulty 

 referred to above is in making Stomatopora a multiserial as well as 

 a uniserial group. Ey accepting the genus Frobnscina, I find that I 

 can arrange the biserial Stomatoporce of the lied Chalk, and keep in 

 accord with the Liassic and Jurassic features of typical forms : 

 whereas by accepting recent biserial Stomatopora' as typical ex- 

 pressions we altogether ignore facial differences that ought to be 

 recognized, palicontologically at least. Undoubtedly in IMesozoic 

 rocks generally uniserial f^tomatoporo' gradually glide into Pro- 

 bosciiw, as Proboscina in some few cases fades into Diastopora. To 

 formulate mere arbitrary divisions, therefore, in the present state of 

 our knoweledge is useless ; yet the study of fossil Polyzoa will be 

 greatly facilitated if, understanding these ])eculiarities, the student 

 accepts certain generic terms as expressions of growth rather 

 than as fixities. The uniserial iStomatojwnt' of the lied Chalk 

 are, however, a distinct group of fossils, and they very rarely, if 

 ever, pass into biserial forms. The Probosc'nui\ as a matter of course, 

 begin their existence as uniserial k^tomaUporn' ; but very early in 

 their development they pass into bi- and multi-serial varieties. The 

 Diastopora of the Red Chalk also have the occasional Proboscinal 

 features ; but the disc-like character of the genus is very constant 

 in all those forms which I place in that division. I have studied 

 these varied and varying changes in all the forms indicated, on 



* Die liryozoeu dor wi-issen Schreibekivido dor Tnsel Riigcn. 1887, p. 8. 



