FROM THE ZONE OF AMMONITES ANGULATUS. 



23 



in each calice, ten large and ten small. The internal ends of the large septa are rounded 

 and swollen out. 



Diameter of the calices Ij inch. 



M. D'Orbigny considered the swollen ends of the principal septa to be pah, and placed 

 the species in the genus Sfephanoccenia, but M. de Fromentel detemiined the correct 

 position of the form to be amongst the " decemeral" Astroccenise.^ 



The species does not appear to have been formed from very perfect specimens, and 

 in M. J. Martin's admirable plate the septa are all equal in length and thickness, and the 

 calices are close together. It is impossible to determine from either the description or the 

 plate whether the calices are deep, whether there is any ornamentation, or whether the 

 ccenenchyma is marked in any way. There are many species of Astrocoenia which are 

 massive, and their formation from superimposed layers is the result more of a process of 

 mineralization than of growth. The form is readily recognisable in its strata, because it 

 is rare and as yet the only species discovered ; but placed in comparison with others from 

 distant localities it is hardly to be distinguished, on account of its defective specific 

 distinctive peculiarities. The Astrocceniae of the Sutton Stone, and from Brocastle, 

 show the smaller septa joining the larger more or less, but this does not appear to be 

 the case in A. Sinemuriensis. The enlarged state of the septal ends is common to several 

 Astrocoenise. It is very probable that with more complete specimens, the occasional 

 union of the septa will be observed in A. Sinemuriensis, for in some specimens of most of 

 the species this non-union is seen in certain calices. 



Specimens of some Astrocceniae in the Sutton Stone and Brocastle beds put on all the 

 appearances of this species when worn. It is therefore introduced here ; but not figured." 



The genus Astrocoenia was formerly included in the Eusmilina aggregata^ but 

 Reuss* pointed out the fact that the upper margins of the septa of the species falling 

 under his observation were dentate and not smooth. 



M. de Fromentel* discovered in the Neocomian formation some species which had 

 dentate septa ; and after acknowledging Reuss's discovery, he placed the genus amongst 

 the XXVth family of his classification, the " Astreens." This family corresponds in part to 

 the AstrcBacecs of Milne-Edwards and J. Haime, and the genus may be considered to 

 form a part of the AstrceacecB. 



In the Introduction to the British Fossil Corals," Astroccenia, being placed amongst 

 the EusmilincB, follows the genus Styhccenia, and was evidently considered to be closely 

 allied to it. The following is the generic diagnosis by MM. Milne-Edwards and J. Haime : 



1 Pal. Strat. de Infra-lias, p. 94. J. Martin, 1860. 



2 See " Remarks on Astrocoenia Sinemuriensis and Asfroecenia Oppeli," Laube, in my essay on the 

 " Madreporaria of the Infra-Lias of South Wales," ' Quart. Journ. Geol. Soc.,' Feb. 1867, *p. 25 (note). 



3 Reusa. ' Beitrage, zur Charakteristik der Kriedescbichten.' 

 * E. de Fromentel, ' Introd. a I'Etude des Polyp. Foss.' 



5 ' Introd. to Brit. Foss. Corals : Palseontogr. Soc' 



