340 PALEONTOLOGY OF ILLINOIS. 



while small acanthopores are only occasionally present. The 

 apertures of the Booecia are closed by centrally perforated plain 

 or radially striated opercula. 



This family is proposed provisionally for the reception of the 

 three genera Callopora Hall, (restricted, Ulrich), Calloporella, 

 and Aspidopora, which have the above noted peculiarities in 

 common. The opercular covering of the zooecial aperture is 

 considered the principal distinguishing feature. The genera are 

 separated by easily recognized characters, Callopora having a 

 ramose zoarium, thin walled, polygonal or sub-circular zooecia, 

 a varying number of mesopores, and no acanthopores. The 

 last structures are developed in moderate numbers in both 

 Calloporella and Aspidopora, the zoarium in both again being 

 discoidal and free, with a concentrically marked epithecal mem- 

 brane on the concave under side. The first is distinguished 

 from the second by having thick ring-like walls to the zooecia 

 and different mesopores. 



(4) TREMATOPORID.E: Ramose, irregularly frondescent, or para- 

 sitic zoaria pertain to forms of this family. The zooecial tubes 

 are thin- walled, adjoining and prismatic in the "immature" 

 region, subcylindrical or more or less completely isolated by 

 abundant angular mesopores in the "mature" region. The 

 zocecia apertures are circular, oval, or petaloid, with a more 

 or less distinct peristome, while the mesopores are closed at the 

 surface by numerously perforated closures, the perforations ap- 

 pearing as small hollow spines or granules. Both sets of tubes 

 are intersected by horizontal diaphragms, but acanthopores are 

 often wanting. Neither cystiphragms nor opercula have been 

 observed in any of the species. 



The family comprises a number of peculiar and several very 

 beautiful Bryozoa, that suggest affinities, more strongly than 

 any other Palaeozoic genera, with Mesozoic types of the TRE- 

 POSTOMATA. Thus Trewatopora compares well with Heteropora 

 and other genera of that type, while Constellaria and Stellipora, 

 closely resemble d'Orbigny's genera Multicava, Domopora and 

 Radiopora. 



The family includes besides the three genera already mentioned 

 also the new genus Nicholsonella, Idiotrypa, and most prob- 

 ably Dittopora of Dybowski. The last is little known, and I 



