58 



THE GEOLOGIST. 



ricms, whicli resembles the preceding in the development of tlie 

 inner walls of its corallites, but differs from them, and allies itself to 

 the next by its mode of reproduction, which is exclusively calicinal. 

 This gemmation, as it is called, is a very interesting and instructive 

 feature. Gyathojphyllimi truncatum is a good example of it. I have 

 often picked up this coral in a Dudley, or Wenlock lime-quarry, 

 in which the parent — a simple, but somewhat angular shaped 

 cup — has been smothered by the growth of young buds from out 

 its calice. Indeed, in many specimens I have seen, these un- 

 natural children have in turn borne young, and a tall turbinate 

 mass of corallites, with calicos mis-shapen by crowding together, 

 has grown up. 



The last division of the " cup- and star-corals" includes those com- 

 posite species that have a common basal plate, and grow by accre- 

 tional development. Strombodes typus is the best known. The 

 star-headed terminations of its corallites cover the surface with ir- 

 regular polygonal figures, the value of whose angles would puzzle old 

 Euclid himself. This species has vertical internal radii, thus differing 

 from its ally, S. Murchisoni, whose inner structure is completely vesi- 

 cular. Another species, S. PhilU^sii, has elegantly shaped caHces, 

 having their angles gracefully lengthened ; while the perfection of 

 beauty is attained by 8. diffluens, whose surface, exhibiting no trace 

 of walls dividing the corallites, is covered with the most exquisite 

 septal floriations. 



Nearly allied by form of calice to the cup-corals are the Fungidce, 

 or "mushroom-corals," an outstanding group of which one genus only 

 seems to have lived in Silurian seas, Pcdceocyclus it is called, i.e., 

 ancient circle. P. poiyita has a quoit-like corallum, thii'ty large 

 septa alternating with a like number of smaller ones, and a curved 

 peduncle-foot of attachment. P, jprceacutus is about the size, 

 and not much thicker than a sixpence, has forty-eight uniform 

 septa, and no peduncle. P. Fletclieri is about half an inch high, 

 has a strongly curved peduncle, and well marked accretion-wiinkles ; 

 superior height gives it advantages, you see. But P. rugosus is 

 taller still, somewhat top-shaped, and has a small peduncle, oddly 

 turned up. 



I have now to describe the milleporal corals, the second great 



