Fistulipora incmstans, PhilL (F. minor, W'Goy). 239 



internal structure that in some of the forms relates them 

 closely to Fistulijjora. I also find this same trilobed form of 

 cell-mouth present in two genera of Carboniferous organisms 

 formerly placed with the Polyzoa ; these are Salcoretepora 

 parallela, PhilL, S. rai-icosta, M'Coy, and Ooniocladia cellu- 

 lifera, Eth., Jun. On sectioning these forms I find that 

 they have a series of vesicular cells in the interspaces 

 between the autopores, as found in the Cystodictyonidas, 

 Ulrich, and T have now placed them in that family (Edinb. 

 Geol. Soc. Trans, vol. v. p. 461, 1887). As stated in my 

 former paper in the ' Annals,' I find also that the trilobed 

 condition of the cell-mouths is characteristic only of the 

 younger stages of the organism in Fistidipora. In the older 

 stages of growth, or where it forms thick crusts in which the 

 tubes of the autopores become more erect, the cell-mouths 

 are seen to be more or less circular in form and to have a 

 slightly raised lip or rim all round the margin of the 

 openings. As there is thus so much difference and variability 

 in the form of the mouths of the autopores in the younger 

 and older stages of the organism, I do not feel inclined to 

 place any value on this trilobed form of the cell-mouth as a 

 generic character, as is done by Messrs. Nicholson and Foord, 

 especially when we find that it occurs amongst a group of 

 organisms that do not seem to be generically related to one 

 another in every case, although the above authors would 

 place some of Mr. Ulrich's forms with Fistuliporce that 

 possessed this character. 



The closing of the mouths of the autopores in F. incrustans 

 by a calcareous cover or operculum is a character that I have 

 lound in specimens from various localities and in several 

 stages of growth. These opercula are seen to be more or less 

 convex on their upper surface, and are perforated in their 

 younger stage by a small transverse opening that becomes 

 obliterated or filled up by the organism in the older stages. 

 Mr. Ulrich also notices these perforated calcareous opercula in 

 his paper above mentioned, and finds them also in one species 

 of I'istidipora, F. clausa, n. sp. He, like myself, is inclined 

 to regard them as the beginning of the successive tabula) 

 that show tliemselves in vertical sections of the tubes of the 

 autopores. Their rarity at the surface in the tubes of most 

 specimens is easily accounted for by the somewhat sparse and 

 wide intervals that exist between the tabulee in many cases, 

 and also often depends on whether the organisms had lived 

 onwards for a period after the formation of the opercula ; 

 in that case they would be found deeper in the tubes and 

 not observable at the surface. 



17* 



