HARDWICKE'S SCIENCE-GOSSIP. 



15: 



times calcareous: they frequently stand upon short 

 footstalks rising from a tubular stock, which creeps 

 over the surface of stones and aquatic plants, in the 

 same way as the horny stems of many of the hydroid 

 polypes. In other cases the cells are sessile, forming 

 a crust upon submarine objects, whilst in others the 

 colony is attached only by its base, with the opposite 

 extremity floating freely in the water. In these the 

 stock is more or less branched, and often leaf-like. 

 . . . The cells are generally partially free ; but in 

 some of the stony species they form a calcareous 

 mass, presenting some resemblance to true Corals, 

 from which, however, they may always be distin- 

 guished by the absence of the calcareous partitions 

 which the latter invariably exhibit."* 



Fig. 141. Cell-Structure of Retef>ora, 

 from Coralline Crag, Suffolk, 

 a. fenestrule. Nat. size i of inch. 



Fig. 142. Two cells 

 of Fciiestellafor- 

 inosa, highly 



magnified. 



The Tiinicafa have no known fossil representatives, 

 on account, probably, of the absence of those hard 

 parts which were most likely to be preserved ; but 

 the Polyzoa have fossil representatives, ranging from 

 the lower Silurian rocks up to the Post-Tertiary, and 

 family connections connecting the living Polyzoa of 

 to-day with families which long ages ago had become 

 extinct. 



The ordinary divisions of this important class have 

 reference chiefly to living genera, or to genera which 

 can be traced backward in time, connecting the living 

 with the fossil species. To follow the subject still 

 further backward, it is necessary that we should take 

 in the whole class and allow the old to piece in with 

 the new, and thus form a connected group, whether 

 that group, or portions only of that group, may be 

 designated either fossil or recent. It will be well, 

 therefoi'e, to confine our attention to one arrangement 

 of the Palpeontological record, rather than to many ; 

 and the student who desires to enlarge his knowledge 

 of the past may very appropriately study the affinities 

 of those genera named in the list which belong to the 

 living Polyzoa of our present seas. 



M. Pictet, in his Palaeontology, divides the Polyzoa 

 into two groups. One (A) called the Cellulina or 

 EsCHARlD.T, group ; the other (B) called the Cen- 



* W. S. Dallas, F.L.S. " Invertebrated Animals." 



TRIFUGIN.E or TUBULIPORID^ group. Tlicse are 

 again subdivided into families. 



A. — The Cellulina. 



Family I. — Cellarioid^e, of which the genera 

 Electra, Electrina, Caberea, Reteplectrina have no 

 known fossil species ; Cauda, Cellaria, Tubucellaria, 

 with fossil representatives. 



Family II. — Escharoidea : Lanceopora, Tere- 

 bripora, no fossil species ; Vincitlaria, Eschara, Lu- 

 nulites, Rdcpoi-a, Cellepora, Vincularina, Porina, 

 Escharifora, Discoporella, Steginopora. Some of 

 the genera in this list have fossil species ranging from 

 the Palaeozoic rocks to the present seas, or to the 

 cretaceous formation. 



Family III. — Flustrinoida : Siphonella, Flus- 

 trella, Flustrina, all with fossil representatives. 



Fig. 143. F./onnosa (Hurst, Fig. 144. Fenestclla imifii- 



Vorkshire), showing fenes- lata (Phillips). Nat. 



trule at bifurcation. Nat. size ^-^ of inch. Pori- 



size yV of inch. ferous face, imperfectly 



rubbed, showing both 

 the inner chamber and 

 also the mouth of cell 

 undulating the margin. 



B. — The Centrifugin^. (The Cyclostomata of 

 Busk). 



Family I. — Radicell.'E : Crisea, Unicrisia. 



Family II. — Operculin^ : Nodelea, and the 

 extinct genera Melicertites and Elea. 



Family III. — Tubulu'orid.e : Fasciculipora, 

 Frondipora, Berenicea, Idmonea, Tubulipora, Sto- 

 matopora, Hornera, and the extinct genera Theonoa, 

 Fascipora, Spiropora (Cricopora), Diastopora, Cavea, 

 Ceriopora, Heteropora. To these M. Pictet appends 

 the following extinct genera : Fenestella, Synodadia, 

 Glauconome, Piilodycda, Seriatopora, and Oldhamia. 

 Below these, Professor Huxley is of opinion, the 

 family of Graptolites ought to be placed.* 



In dealing with the Carboniferous Polyzoa, the only 

 genera I shall have to illustrate and describe in the 

 above list are those printed in italics. The list will 

 be useful to the scientific student, and those who 

 wish to follow up the study will do well to refer to 

 Mr. Busk's arrangement as given in his "Crag 

 Polyzoa " and museum catalogues. 



Fenestella. — This genus, as restricted by Lons- 

 dale from Miller's MSS., so far as is yet known' 



* Jukes's •' Manual of Geology," pp. 367-8. I have not 

 mentioned the sub-genera, extinct and living, as given by 

 Jukes. 



