342 PALEONTOLOGY OF ILLINOIS. 



to Homotrypa of the MONTICULIPORHLE; second, several species 

 of Stenopora to the AMPLEXOPORIDJE ; and, third, several other 

 species of Stenopora and Anisotrypa to the RHABDOMESONTID.E 

 of Vine. The last comparison, if complete and thorough, es- 

 tablishes a close chain of connecting links between the TREPO- 

 STOMATA and CYRPTOSTOMATA. 



(6) AMPLEXOPORID.E. The zoarium in this group, comprising 

 the genera Amplexopora, Monotrypella, Petalotrypa, Lepto- 

 trypa, Atactopora and Discotrypa, may be ramose, bifoliate, 

 encrusting, massive or discoidal. The zocecial characters are 

 more simple than in any other family of the suborder, the 

 colony being composed of subequal, usually thin-walled, pris- 

 matic tubes, crossed by variously disposed horizontal dia- 

 phragms. The divisional line between adjoining zocecia is 

 generally distinctly marked, and in a few cases, (e. g. Mono- 

 try pella crassimuralis) the zocecia become rounded near surface, 

 leaving triangular tabulated interspaces, that closely simulate 

 mesopores in vertical sections. True mesopores are, however, 

 wanting, but small abortive cells, usually filled internally by a 

 calcareous deposit, sometimes occur among the zooecia forming 

 the monticules. Acanthopores are absent in Discotrypa, but 

 in the other genera they are more or less abundant and some- 

 times conspicuous. 



On account of the simplicity of construction, we are forced to 

 depend very largely upon zoarial variations in dividing the 

 family into generic groups, Of microscopic characters the pres- 

 ence or absence of acanthopores is of the first importance in 

 distinguishing the genera. 



(7) DIPLOTRYPID^E. This family is proposed provisionally 

 for the reception of Diplotrypa, Batostoma and Monotrypa, 

 three genera that have given me no little trouble to place 

 satisfactorily. Though fully persuaded that their association 

 in one family is natural, I am still not prepared to discuss 

 their inter-relations and affinities with other Bryozoa. 



(8) CERAMOPORID^. In the typical genera of this family the 

 zoaria form thin parasitic expansions, but other modes of 



