THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE III. VOL. III. 



No. VII.— JULY, 1886. 



OEIGIUAL AETICLBS. 



I. — On Desmidopora alveolaris, Nich., a New Genus and 

 Species op Silurian Corals. 



By H. Alleyne Nicholson, M.D., D.Sc, 



Eegius Professor of Natural History in the University of Aberdeen. 



(PLATE VIII.) 



Desmidopora, gen. nov. 



Gen. Char. — Corallum composite, with an epithecate base, the 

 corallites subpolygonal, and indissolubly united by the coalescence 

 of tbeir walls. The corallites are sometimes circumscribed, but they 

 are for the most part more or less extensively connected by deficiency 

 of their walls in particular directions, so as to give rise to sinuous 

 rows of serially-united tubes. The calices, like the corallites, may 

 be circumscribed, but are mostly in the form of vermiculate grooves 

 corresponding with the serially confluent corallites. The calices 

 are not oblique, nor are the corallites reclined. Mural pores are 

 numerous and well developed. Septa and septal spines are wholly 

 wanting. The tabula? are numerous, being simple and complete in 

 the circumscribed corallites, but becoming vesicular in the rows of 

 serially confluent corallites. New corallites are produced by fission. 



I have found it necessary to propose the above generic name for 

 a remarkable coral from the Wenlock Limestone of Dudley, for 

 specimens of which I am indebted to the kindness of Mr. William 

 Madeley, whose experienced eye had recognized that they belonged 

 to an unusual type. In general aspect, the specimens show resem- 

 blances to the laminar forms of both Alveolites and Chcetetes, as also 

 to Labechia ; and it was to the last of these that I was at first dis- 

 posed to refer them. A microscopical examination has, however, 

 shown that they are most nearly related in reality to Alveolites ; the 

 presence of numerous mural pores, quite of the type of these struc- 

 tures in Favosites itself, proving that they are indubitably referable 

 to the group of the Favositidge. The specimens, however, exhibit 

 the following structural peculiarities, which preclude our referring 

 them to any previously-named genus of Favositoid Corals with 

 which I am acquainted : — 



(1.) The primordial wall of the corallites is entirely wanting, 

 adjoining visceral chambers being thus separated by an apparently 

 single wall, as is the case in the genus Chcetetes, Fischer. 



DECADE III. — VOL. III. — NO. VII. 19 



