688 



SILURIAN CORALS. 



muriatic acid ; and in the flame of a taper preserves its structure, but assumes a ferruginous 

 colour. Fused with carbonate of soda, it forms a pale greenish enamel. Its developement is 

 apparently due to decomposition. In some specimens it is very thin (see centre stem, f. 12 c), 

 in others of great relative thickness, and in this case the inner boundary is generally irregular 

 in outline (upper stem, f. 12 c). Occasionally the change has penetrated nearly to the centre 

 of the coral, which then consists of insoluble, reticulated, yellowish fibres, or interrupted la- 

 mellae j and an interval is presented between the matrix and the fossil (right hand stem, f. 12 c), 

 Formation and locality. Llandeilo Flags, Robeston Walthen, Pembrokeshire. 



Porites discoidea, sp. n. Lons. PI. 16. f. 1 nat. size. 



P. Disk-shaped, stars not defined, composed of interrupted lamellce. 



This specimen is apparently much worn, and from the disposition of the rays it is difficult 

 to count them accurately, but they appear to be twelve in number. 



The specimen is in the collection of Mr. Bowerbank. 

 Formation and locality. Wenlock Limestone, Wenlock. 



Monticularia, Lamarck. 



Monticularia conferta, sp. n. Lons. PI. 16. f. 5, 5 a. — 5 upper surface nat. size, 5 a vertical 

 weathered surface. 



M. Encrusting or expanded in lobes ; central axes close-set, irregular in size, yet large in 

 proportion to the distance between them; round when single, but several are often united ; indi- 

 cations of radiating lamellae few under surface when free, uneven, smooth or marked by 

 irregularities of growth. 



Formation and localities. Wenlock Limestone, Benthall Edge, and Gleedon Hill, near 

 Wenlock. 



ASTREA. 



Ehrenberg, in his memoir on the zoophytes of the Red Sea, confines the genus Astrea to 

 those corals, the animals of which possess the following characters : " pallio Stellas contiguas 

 distinente nullo, disci ipso margine prolifero, ore divisione spontanea bipartite ; " and he places 

 those which have contiguous stars, but are quadripartite, " ore divisione spontanea quadripar- 

 tite," in the genus Favosites. This arrangement I have not been able to adopt, with reference 

 to the latter genus, which has been used in this catalogue for corals of a very different descrip- 

 tion (see F. Gothlandica, &c), and in conformity with the application of approved authorities. 

 In the genus Astrea, have therefore been placed the fossils, which exhibit a natural subdivision 

 of the old star, leaving the final determination of their proper arrangement to those who are 

 qualified to make the necessary separations. 

 Astrea ananas, De Blainville, PL 16. f. 6, 6 a to 6 /. — 6 nat. size, 6 a to 6 /developement of young 

 stars, nat. size. 



Syn. and Ref. Madrepora, Fougt, 1745 ; Linn. Amoen. Acad. t. 1. p. 196. fig. 8. 1749. 

 Madrepora ananas, Linn. 10th Edit. t. 1. p. 797- 1758 ; Gmelin, p. 3764 ; Parkinson, Org. 

 Rem. vol. 2. p. 40. PI. V. f. 1. 1808. 



Madrepora hexagonatus ?, Schlotheim, Petref. p. 360. 1820. 



Cyathophyllum ananas, Goldfuss, Petref. p. 60. Tab. XIX. f. 4. 1826 j Milne Edwards, 2nd 

 Edit. Lamarck, t. 2. p. 429. 1836. 



Astrea (Favastrea) Baltica, De Blainville, Man. d'Actinologie, p. 375. 1834. 



Fig. 6 a to 6 d beautifully illustrate the subdivision of the old star, and the gradual develope- 

 ment of four young ones. Fig. 6 a exhibits the cross lines, marking the subdivision of the animal ; 



