354 ZOOPHYTES. 



and CyathophyllidEe. In the former, when the cells are not contiguous, 

 the limits of the stars are formed by a thickening and lateral coales- 

 cence of the radiating lamellae; and the interstices, in a transverse 

 section, constitute a narrow band, often cellular, between the several 

 stars : but, in the latter, although there may be broad interstices 

 between the cells, there are none between the stars ; they are sepa- 

 rated only by a simple thread-like line. The lamellae often become 

 subdivided, and are united by numerous cross dissepiments. It 

 appears therefore that there is a decided difference in the structure of 

 the polyps. In Astraeas with contiguous cells, we have in a transverse 

 section nearly the same structure as in the Cyathophyllidae ; but, 

 unlike the species of the group before us, they are dichastic in 

 budding, the disks of the polyps gradually subdividing by growth. 

 The interstitial buds of this family are in character like those of the 

 Porites and Astroites, in which budding is lateral. The summit-buds 

 of the Cyathophyllidse (J 81), differ decidedly from the disk-buds of 

 the Astraeas. Their production is attended with a sacrifice of the 

 parent, and they consequently grow up as prominent young, like the' 

 lateral buds of a Caryophyllia ; while in the Astrseas, without the 

 intermitted mode of growth and reproduction, and a prolate growth of 

 the summits, the young and parent grow on together, with an equal 

 rate of increase. 



The Cyathophyllidse afford examples of both aggregate and segre- 

 gate zoophytes. Some species form clumps of branches like those of 

 many Mussse and Euphyllise; while, in others, the adjacent polyps 

 coalesce and produce solid massive forms. In a few, the polyps are 

 crowdedly in contact, without coalescing, and in consequence of the 

 mutual pressure, have a prismatic form ; and the coralla, though ap- 

 parently solid, may be readily broken into prisms. The same genus, 

 as in other departments of zoophytes, may contain both solid, branch- 

 ing, and also simple or non-budding species. 



A study of the internal structure of these corals, has led the author 

 to some changes in the received limits of groups, and also to the intro- 

 duction of one or two new genera. The generic names of older authors 

 have, in some instances of late, been misapplied : in obedience to the 

 principles relating to nomenclature, digested and brought out by the 

 British Association, a restoration to their original characters has been 

 attempted ; and where impracticable, their rejection seemed preferable 

 to retaining them with altered characteristics. 



