Prof. BZ.A. Nicholson — On a New Silurian Coral. 291 



Very closely related to Laceripora, Eichw., if indeed really generi- 

 cally distinct from it, is the genus Somphopora, Lindstr. (" Ober- 

 silurische Korallen von Tshau Tien," p. 51, pi. vii. figs. 2 — 5) ; and 

 tliis, therefore, also presents some resemblances to Desmidopora. 

 In Somphopora, however, the primordial wall of the corallites is 

 persistent, and well-developed septal structures are present, while 

 the mural pores are of very large size, points quite sufficient to prove 

 its distinctness from Desmidopora. 



Beyond the limits of the Perforate Corals, the only genus with 

 which Desmidopora need be compared is Chcetetes, Fischer. In 

 general aspect there is a decided resemblance between Desmidopora 

 and some of the species of Chcetetes ; and the fissiparous mode of 

 increase is a structural feature common to the two genera. There 

 are, moreover, species of Chcetetes (such as C. Etheridgii, Thorns, sp.) 

 in which the corallites in the process of fission become often laterally 

 elongated, and the calices are therefore commonly compressed and 

 sinuous. The presence of numerous well-marked mural pores in 

 Desmidopora is, however, of itself sufficient to separate the present 

 genus wholly from Chcetetes, Fischer. 1 



The only species of Desmidopora with which I am acquainted 

 occurs in the Wenlook Limestone of Britain, and possesses the fol- 

 lowing characters : — 



Desmidopora alveolaris, Nich. 

 Labechia alveolaris, Nich., Mon. Brit. Stromatoporoids, p. 83 (name only), 1886. 



Spec. Char.. — Corallum in the form of a laminar expansion, which 

 may reach half a foot in diameter, and which varies in thickness 

 from less than a centimetre to two centimetres. The corallum 

 was attached to some foreign body by a peduncle, and the base is 

 covered by a concentrically wrinkled epitheca (PI. VIII. Fig. 1). The 

 corallites are directed approximately at right angles to the basal 

 epitheca, and are usually from -| to 1 millim. in diameter. The 

 calices are variable in shape, but are never oblique or crescentic in 

 form. Parts of the surface generally show many of the calices as 

 as subpolygonal, definitely circumscribed apertures (PL VIII. Fig. 8) ; 

 while in other parts the calices have become more or less extensively 

 confluent, and have the form of winding and sinuous grooves (PI. VIII. 

 Fig. 2). The tabulae are numerous, mostly convex, with their con- 

 vexities turned upwards, and generally about half the diameter of 

 the corallites apart. Very often they are placed at approximately 

 the same level in adjoining tubes ; and in the serial rows of 

 corallites they become vesicular. Mural pores are numerous, but 

 not of unusually large size. 



1 Mr. James Thomson has described mural pores as occurring in Chcetetes Ethe- 

 ridgii, Thorns, sp., C. septosus, Flem., C. depressus, Flem., and 0. hyperboreus, 

 Nich. and Eth., jun. ; and he has therefore referred these species to Alveolites (Proc. 

 Phil. Soc. Glasg. 1881). I have, however, examined numerous specimens and 

 microscopic sections of all these species, and am quite satisfied that the walls of the 

 corallites are in all of them imperforate. Indeed, the figures given by Mr. Thomson 

 himself show conclusively that the structures which he has described as mural pores 

 could not possibly be of this nature. 



