ROB EETS— UPPER SILURIAN CORALS. 



57 



iug, crowd upon each other's limits, and a mass of corallites is the re- 

 sult, whose base is the old parent coral, and whose upper surface is 

 covered by the star-rayed cups of the children. Acervularia ananas 

 is the commonest species of these family corals. 



The polyps that formed these cup-corals grew from their base up- 

 wards, and were probably long hvers, for a well-matm-ed specimen of 

 Cyatlio^hijllum Loveni Avill measure five inches in height, indicating 

 by the number of proruinent edges that surround it — accretion- 

 wrinkles they are called — a long and chequered existence ; for when 

 these are regularly prominent, we infer the polyp led an active life of 

 development. On the contrary, when their irregularity forms annu- 

 lar depressions on the corallum, these indicate the occasional repose 

 of the zoophyte from its work of extension. 



The common species belong-ing to these cup-corals are easily 

 known. CyathojjhjUiim Loveni has very prominent accretion- 

 wrinkles, while upon the sides of C. angustum they are but feebly 

 developed. G. i:)seucloceratites has an oval calice, with only thirty- 

 eight large septa alternating with a like number of smaller ones ; the 

 two former species have sixty of each kind. Omphyma turhinata is a 

 short, wide-mouthed species, with double the number of septa, and 

 has radiciform appendages, i.e., rootlets, attached to its lower end. 

 0. subturhinata differs only in being taller, as its name implies, 

 having but eighty septa, and well developed accretion-vvrinkles. 0. 

 MiLi'cliisoni is nearly alhed, but has vesicles, or bladder-hke tubercles, 

 coming up among the septa. Then there is Goniojjhyllum Fletcheri 

 with a square calice ; Aulacojphyllum mitratum, a small turbi- 

 nated cup, whose principal and rudimentary septa combined only 

 amount to sixty-eight, and Ftycliopliyllum patellatum, with one hun- 

 dred septa, and the border of its calice so much raised that the coral- 

 lum resembles the cap of a mushroom. These are all the simple cup- 

 corals we are likely to meet with in the Wenlock rocks. Among the 

 composite ones is the species I before alluded to, GyatJiophylhim arti- 

 cidatum, generally met with as a mass of tall slender coralhtes, so 

 thin-skinned that their upright internal lines of structure (costce) are 

 clearly visible. SyringojpJiyllum orgamim is another, having star- 

 headed tubes of exquisite beauty ; and as a connecting link between 

 this and the next division of cup-corals, we have Acervularia hixu- 

 VOL. III. H 



