CORALS FROM THE SILURIAN FORMATION. 247 



peduncle. The upper surface much depressed towards the centre, and surrounded by a 

 thick rim formed by prominent septa. The columella (if existing) very short and 

 imperfectly formed. Large septa (28 or 30), uniformly developed, and alternating with 

 smaller ones; they probably form six systems, four of which are composed of seven elements, 

 and two of eleven derivated septa ; or, in other words, they appear to constitute four complete 

 cycla, to which septa of a fifth cyclum are superadded in one half of two or three systems, in 

 which the quaternary septa have also attained a greater size. All these septa are thick, very 

 closely set externally, and quite straight, the upper edge of the principal ones is regularly 

 convex, and armed with closely-set, strong teeth or crenulations ; two rows of these small 

 points often exist on the same septum, towards the exterior part of the corallum. 

 Diameter, in general, 5 or 6 lines ; height about I line. 



Dudley. It is also met with in Gothland. 



Specimens are in the Collections of Mr. T. W. Fletcher, and of Mr. J. Gray, at Dudley, 

 of the Museum of Practical Geology, London ; of M. de Verneuil, at Paris, &c. 



This species differs from P. Fletcheri? and P. rugosus"" by its extremely flat form. 

 P . praacidui is also discoidal, but all its septa are equally developed, whereas, in 

 P. porpita, there are alternately large and small septa. 



2. PaIuEOCYCLUs pr^acutus. Tab. LVII, figs. 2, 2a, 2b, 2c. 



Cyclolites pkjeacuta, Lonsdale, in Murchison, Silur. S^ r , p. 693, tab. xix, fig. 4, 1839. 

 Cyclolites lenticulata, Ibid., p. 693, tab. xv, fig. 5 (but not Porpites lenticulatus of 



Schlotheim). 

 Cyclolites pr^eacutus, Eichwald, Silur. Schisten Syst., p. 201, 1840. 

 Discophyllum fr,eacutum and lenticulatum, D'Orbigny, Prodr. de Paleont., vol. i, p. 47, 



1850. 

 Pal.eocyclus PRiEACiiTUS, Milne Edwards and Jules Haime, Pol. Foss. des Terr. Palseoz. 



(Arch, du Mus., vol. v), p. 205, 1851.— Ann. des Sc. Nat., 

 3d ser., vol. xv, p. 110, 1851. 



The only specimens of this species that we have seen, are those described by 

 M. Lonsdale, and belonging to the Collection of the Geological Society of London. They 

 are cyclolitoid coralla, much resembling P. porpita by their general form, but thinner. 

 Their under surface is almost flat ; sometimes it is slightly prominent in the centre, but 

 never presents any appearance of a peduncle, and is covered with a somewhat thin, 

 delicately-wrinkled epitheca. Septa 48 in number, not much elevated, regularly crenulated, 

 and not appearing to alternate with smaller ones. Diameter of a large individual, about 

 8 lines ; height about 1 line. 



Found at Marloes Bay, Pembrokeshire. 



1 See tab. lvii, fig. 3. 2 See tab. lvii, fig. 4. 3 See tab. lvii, fig. 2. 



