336 PALAEONTOLOGY OF ILLINOIS. 



True CYCLOSTOMATA appear already in the Chazy horizon of 

 the Lower Silurian, from which the author has described Mito- 

 clema cinctosum. This species, though probably belonging- to 

 the same family as Entalophora Larax., differs from species of 

 that genus in several important particulars*. The axial region 

 of vertical sections is more like what we find among ramose 

 TREPOSTOMATA or CRYPTOSTOMATA. 



In the Trenton proper we find already a fair representation, 

 the following genera having been determined: Stomatopora 

 Bronn, Berenicea Lamx., Scenellopora, Protocrisina, Diploclema 

 and Phacelopora, each with one or two species. Individuals 

 of these forms are rather uncommon, but with the beginning of 

 the Cincinnati group both species and individuals become more 

 abundant. Scenellopora is not yet known from these rocks, but 

 another group of species nearly related to Stomatopora, and 

 apparently congeneric with the species for which Audouin pro- 

 posed the genus Proboscina, now make their appearance. In 

 Upper Silurian deposits I have detected only Berenicea (Sage- 

 nella Hall) two species, Stomatopora, one, Diploclema one or 

 perhaps two. For Devonian forms that may belong here, Hall 

 proposes several genera, but no true CYCLOSTOMATA are as yet 

 known from the Carboniferous rocks. Thus it seems that the 

 suborder was better represented during Silurian times than at 

 any subsequent time before the beginning of the Jurassic de- 

 posits. Several interesting facts are brought out by a compari- 

 son of these ancient types with their much more numerous 

 Mesozoic relatives. 



*In a paper on Australian Bryozoa, Mr. A. W. Waters not only thinks Mitoclema 

 the same as Entalophora, but he identifies the Chazy form with E.verticillata Goldfuss, 

 a Cretaceous species. Mr. G. B. Vine (Kep't on Eec't. Poly.), however, thinks the species 

 distinct and only the genera synonymous. These gentlemen arrived at their hasty and 

 erroneous conclusions without examining specimens, and as the internal structure of 

 Mitoclema cinctosum had not yet been made public, they should have deferred their 

 condemnation. When I proposed Mitoclema I was acquainted with over twenty species 

 of Entalophora (Spiropora). All of these possessed one peculiarity which I could not 

 find in my species, namely, all the zooecial tubes of EntalopJiora originate along the 

 axial line of the branch, and gradually increase in diameter as they curve outward 

 toward the surface. An end view of the branch shows the very characteristic arrange- 

 ment of the tubes in intersecting curved radial lines. As I have said, this peculiar ar- 

 rangement is not present in the Silurian species, and I consider myself justified in pro- 

 posing a new generic name for it. 



