BRYOZOA. 337 



Species of Stomatopora and the closely allied divisions Pro- 

 boscimi and Bei-enicea from Cincinnati, Ohio, differ in no appre- 

 ciable manner from Jurassic and Cretaceous species, while 

 Mitoclema, Diploclema, Protociisina, and Scenellopora, closely 

 resemble Entalophora, Bidiastopora, Crisina, and Defrancia, re- 

 spectively. Of all the Silurian forms the two species of Phace- 

 lopora are probably the most distinct, yet, even these admit of 

 comparison with some of the TUBULIPORHXE. 



The large size of most of the Devonian forms makes it some- 

 what doubtful that they are really Bryozoa, still their general 

 aspect is so much like that of typical CYCLOSTOMATA that I do 

 not see how they can be placed elsewhere. To determine the 

 question beyond dispute requires a more minute study than I 

 have found time to give them. 



III. TREPOSTOMATA: The zoaria of this suborder are com- 

 posed of prismatic or cylindrical tubes, that change more or 

 less in character as they pass from the "immature'' into the 

 "mature" region. In the ''immature" region the tubes have 

 extremely thin, prismatic and simple walls, while horizontal 

 diaphragms may or may not be developed here. The "immature" 

 region of a zooecial tube is longer in the ramose forms, than 

 in the lamellar and parasitic, and is equivalent to the primitive 

 cell of the CHILOSTOMATA and CRYPTOSTOMATA. The transition 

 from the "immature" to the "mature" condition is often grad- 

 ual, but more generally rather abrupt, though never so much 

 so as in the CRYPTOSTOMATA. The change consists of (1) a 

 thickening of the walls, (2) the development of mesopores, and 

 (3) an increase in the number of diaphragms. Opercular struc- 

 tures and perforated diaphragms also only occur in the mature 

 region. Each stage in this region marked by the diaphragms, 

 represents a layer of zooecia, each of the individual chambers 

 having been developed in direct sequence from the zooecium im- 

 mediately beneath it. By repeating the process a tabulated 

 tube resulted. 



This suborder, though having living representatives, attained 

 its irreatt'-T development during Palaeozoic times. In Mesozoic 

 and more recent times the distinctive characters are largely 

 subdivided, and, by equal concessions on the part of the CY- 

 CLOSTOMATA, the dividing line between the divisions has become 

 -42 



