PROF. P. MARTIN DUNCAN ON MICRABACIA CORONULA. 561 
38. On the InvtERNAL Srructurrs and Crassiricatory Positron of 
MicraBacta coronvia, Groldfuss, sp. By Prof. P. Marrin 
Duncan, M.B. (Lond.), F.R.S., F.G.8., &. (Read June 11 
1884.) 
MicraBacta coronvta, Goldfuss, sp., called Cyclolites by William 
Smith (1816), is a characteristic fossil of the Upper Greensand, and 
has been found at Warminster and, according to W. Smith, at Chute 
Farm and Paddle Hill, near Dunstable, and in the beds at Essen and 
Le Mans; it is also found in the‘ Cambridge Greensand.” Bolsche 
has described a Micrabacia from the Senonian. 
The external characters of the species have been beautifully deli- 
neated by Milne-Edwards and Jules Haime, in their monograph of 
the British Fossil Corals *, and the description of the specimen used 
as a type is, as might be anticipated, careful and correct. Allowing 
for variation in some parts, the description permits any specimen 
to be recognized, specifically, from the appearance of the external 
structures. It does not appear that these authors made sections of 
this coral, and as their work was classificatory and not necessarily 
morphological, they probably did not think it necessary to investi- 
gate the internal structures specially. 
The generic diagnosis of the type was also carefully given by 
Milne-Edwards and Jules Haime, and the genus Micrabaca was 
separated from the genus Mungia, Dana, by them. 
They placed the genus in the family of Aporose Corals called 
Fungide by Dana, and in their own subfamily Fungine, which 
includes Fungidee with perforated walls. The generic and specific 
diagnoses and the synonymy are given in the ‘ Histoire Naturelle 
des Coralliaires,’ vol. 11. p. 29. 
After the careful descriptions of these authors had appeared, came 
the work of M. de Fromentel, entitled ‘ Introduction a l’Ktude des 
Polypiers Fossiles,’ 1858-1861. It does not add anything to the 
knowledge of the genus or species, and merely complicates the 
classificatory position by uniting the form with others which are 
morphologically distinct. 
Many years since the late Dr. 8. P. Woodward directed my atten- 
tion to the species, and to its interesting resemblance to a discoid 
Stephanophyllia. 
On working at the subject I was not so impressed as my teachers, 
MM. Milne-Edwards and Jules Haime, had been of the impor- 
tance of the remarkable arrangement of the coste in Micrabacia 
coronula, because some Australian corals, with which I was then 
familiar, indicated that the peculiarity could or could not exist in 
different species of a genus. Subsequently, thus influenced, I de- 
scribed Micrabacia Fittoni, a new form from the Gault of England 7. 
* Pal. Soc. 1880, ‘ British Fossil Corals,’ pt. 1, Tab. x. figs, 4—4a, and p. 60. 
t ‘Monograph of the Secondary Corals of England,’ Pal. Soe. pt. ii. no. 1, 
p. 37, 1866. 
