146 



HARDWICKE'S SCIENCE-GOSSIP. 



in the "small adventitious tubules" which rise from 

 the back of some of the cells. It is well to note this 

 fact, because when we trace the species backward in 

 time this is a most important test. Recently it is a 

 very prolific species, and the geographical distribution 

 is a very wide one, ranging from Spitzbergen to the 

 Adriatic, and in time, according to Professor Dawson, 

 to the Post-pliocene of Canada. According to present 

 observations it is not a deep-water form, for I can find 

 no details of the species being found below twenty 

 fathoms. 



D. patina seems to have been the earliest recorded 

 species, as it was originally described by Lamarck as 

 TitbuUpora patina. This species has many well- 

 marked peculiarities. It is sometimes discoid, cir- 

 cular or elliptical, and more or less of a cup shape. 

 The central cells are immersed and usually closed, 

 the marginal ones are erect and open. These closed 

 cells have given rise to a variety of opinions. They are 

 supposed by some to be representative of the opercular 

 covering, as in the Cheilostomata, and they are present 

 in another species to which we shall draw attention 

 l^resently. A very broad basal lamina extends beyond 

 the margins of the species, and is one of the means of 

 its identification. Tlie geographical distribution is 

 also wide, ranging from the North and Arctic seas to 

 the Adriatic, and in depth from five to one hundred 

 and seventy fathoms. At Shetland, according to 

 Barlee and Norman, it is frequently taken at the latter 

 depth, and here also the forms are proliferous ; that is . 

 to say, fresh colonies are produced on the margins of 

 the older colony — a peculiarity of habit that may be 

 traced back to species which were living in Oolitic 

 times at least, and doubtfully even in the Carboni- 

 ferous era. 



Our next and last British species is D. Sarnicnsis, 

 Norman. Of this species Busk gives no descriptive 

 text, but on Plate 34* he gives a very good figure. 

 There is a striking peculiarity about some of the cells 

 of D. Sarniensis, which will justify a more detailed 

 account than I have giten of the other species. 



In his original description, Mr. Norman t said 

 tliat it "consisted of a milk-white opaque punc- 

 tured crust, spreading upon shells with a round or 

 lobulate outline, and sometimes reaching % inch 

 in diameter." The most striking peculiarity however 

 is where he describes that " Here and there among 

 the open mouthed cells, there occurs a tube which, 

 instead of being open, is closed above with a little 

 cap, from one side of the centre of which rises an 

 umbonal-like process, which is perforated at the apex. 

 Probably these organs are connected with the repro- 

 duction of Diastopora, and are homologous with 

 ovicells." As many of the Diastoporae both recent 

 and fossil, and also other members of the family 

 Tubiliporidoc have their ocecia as an inflation of the 

 surface of the zoaria, these peculiar cells, both in 



• " Cyclostomata. " 



t Ann. Mag. Nat. Hist., January, 1864. 



D. patina and D. Sarniensis, have given rise to a very 

 pleasant piece of speculation. It will be seen that 

 Norman suggests that they may be reproductive cells, 

 or the homologues of the ovicells. Mr. Hincks says,* 

 "The precise significance of the zooecia which are 

 operculate, and furnished with the small tubular 

 process at the top, is unknown .... and D. Sarniensis 

 is furnished abundantly with ooecia of the usual 

 character." In another part,tin describing D. patina, 

 Mr. Hincks says, " It is difficult to determine what 

 the precise function may be of the closed cells, which 

 occur in such numbers in every colony. Smitt 

 has conjectured that they may be connected with 

 the production of Spermatozoa, and notes that in 

 D. patina there is sometimes a small tubular opening 

 in the cap or operculum, analogous to the projecting 

 process in D. Sarniensis. It may be objected to this 

 view that the closed cells are so numerous as to be 

 out of all proportion to the function assigned to 

 them ; but it would be difficult to suggest a better 

 interpretation, and it will do good service by giving 

 direction to inquiry." 



In describing ReticuUpora dorsalis. Waters, the 

 author draws attention to similar tubules. " On the 

 dorsal surface all the cells I have examined have a 

 cover with a projecting tubule in the centre : and on 

 other cells they are very frequent. Similar covers 

 are found on many of the Cyclostomata j but from 

 their frequency. . . I doubt if their significance is fully 

 understood." t Mr. Busk mentions "a minute 

 central perforation," in the calcareous lid of some of 

 the cells in Mesenteripo'ra.% Professor Braun, in his 

 very able paper on the Polyzoa of the Middle Jura, 

 speaks of these opercular cells as a special feature of 

 Elea foliacea, and since then Mr. F. D. Longe, 

 F,G.S.,|1 has drawn attention to certain Escharoid 

 forms of Oolitic Polyzoa for the purpose of showing 

 the apparent or real relationship between the 

 Cheilostomatous and Cyclostomatous forms. There 

 are very similar calcareous opercula found in some 

 of the species of Glauconome, Polypora, and Fenestella 

 of the Carboniferous series ; and whatever their 

 significance may be they must not, in any sense, be 

 confounded with the horny opercula of the Cheilo- 

 stomata. For the purposes of classification of the 

 latter group, Mr, Waters has made a very minute 

 study of the opercula of a great number of species, 

 and he finds that so constant are several typical 

 features that whole genera may be arranged under a 

 few general heads, independent of the presence of 

 other characters pertaining to the genera. Thus he 

 says that some of the Lepralia have opercula ap- 

 proaching to the character of Cellepora, whilst other 

 species of Lepralia approach by their opercula to 

 those found in certain species of Eschara and 



* " British Polyzoa," vol. 

 t Ibid. p. 460. 



, p. 464. 



X Ann. Mag. Nat. Hist. i?79, p. 278. 



5 "Crag Polyzoa," p. no. 



Jl " Geological Magazine," January, 1881. 



