FROM THE GREAT OOLITE. 



181 



taken from the coralliferous layer in the Combe-Down quarry by my 

 friend Mr. T. J. Slatter. 



Genus Helioc(enia. 



Heliocoenia, Etallon, Etud. Paleont. Terr. Jurass. Haut-Jura, 

 p. 74 (1859). 



Placocoenia, d'Orb. ? 



M. d'Orbigny formed the genus Placoccenia from a cast of a coral 

 somewhat like Stylina, but differing from it in having a lamellar 

 columella. His description is very brief, and the genus is not suffi- 

 ciently particularized for adoption, though there is some probability 

 that the subsequently created genus Heliocoenia is identical with it. 



The want of figures to illustrate Etallon's descriptions of Heliocce- 

 nice has been supplied by M. Koby, in his fine work on the Jurassic 

 corals of Switzerland*. Eive species are therein figured, one of 

 which, Heliocoenia costidata, Koby, has a small, styliform columella 

 and appears to me to differ so much from the others as to be doubt- 

 fully referable to the same genus, 



M. de Eromentel, while acknowledging the genus Placocoenia of 

 M. d'Orbigny, does not admit Heliocoenia, but has created a very 

 closely allied genus, Stylohelia. This latter has been merged into 

 Heliocoenia by M. Koby. 



Prof. Duncan, while ledudiig Heliocoenia to the rank of a subgenus, 

 has placed it in his " Alliance Styloid a" t, immediately following 

 Stylina. The genus Placocoenia^ which I have supposed to be identical 

 with Heliocoenia^ he introduces into another " alliance," which he 

 designates " Placocoenoida." Further, he separates the genus Stylo- 

 helia entirely from the foregoing, and associates it, with EnalloTielia 

 and Dendrohelia, in the family OctrLiifiD^. 



In direct coatrast to the views of Prof. Duncan, M. Koby unites 

 Stylohelia and Heliocoenia in one genus, giving the latter name the 

 preference on account of its priority. With specimens of Stylohelia 

 mamillata before me, which I have received from the Corallian of the 

 Haute-Saone, I feel no hesitation in associating the genus Stylohelia 

 with Stylina and other allied genera, but fail to observe any alliance 

 whatever with the Oculhstid^. 



Helioccei^ia oolitica, n. sp. (Plate Y. figs. 15-17.) 



The corallum has a somewhat peduncular form, with an irregu- 

 larly flat but not overhanging top. The calicos are very unequally 

 distributed over the whole corallum, but are very thinly scattered on 

 the peduncular portion. On the top they are thinly placed, excepting 

 where gemmation has taken place most recently, where they are 

 rather crowded. They have not much prominence, and the interca- 

 licular costae, which are of nearly equal size, meet, but end abruptly 

 in the middle of the intercalicular spaces. 



The septa are exsert, and they and the costse, with which they are 



* Monogr. Polyp. Jurass. de la Suisse, p. 63 (1881). 



t " Eevision of Families and Genera," see pages 45, 110, and 197. 



