468 M. K. A. Zittel on Fossil LitMstidce. 



upper part is sometimes calcified, and the lower, so far as 

 the wrinkled membrane extends, converted into chalcedony. 

 All the species are Silurian : — 



1. Aulocopium aurantt'um, Osw., in F. Rom. Sad. p. 4, 

 Taf. ii. fig. 1 a-c. 



2. Aulocopium diadema^ Osw. ib. p. 5, Taf. i. fig. 1 a-c. 



3. Aulocopium hemisphoericum, F. Rom. ib. p. 6, Taf. ii. 

 fig. 3. 



4. Aulocojnum cepa, F. Rom. ib. p. 7, Taf. ii. fig. 2. 



5. Aulocopium discus^ F. Rom. ib. p. 8, Taf. iii. fig. 1. 



6. Aulocopium cylindraceum^ F. Rom. ib. p. 9, Taf. iii. 

 fig. 2. 



Phymatella, Zitt. 



Scyphia p. p., Rom., Mich., Court. 



Siphonia p. p., Reuss. 



Eudea p. p., Cylindj'osjiongia p. p., Hippalhnus p. p., Rom. 



Polythyra, Hypothyra, ? Physocalpia, Pom. 



Sponge simple, cylindrical, pyriform, flask-shaped or nodu- 

 lar, sessile or long-stalked, with a deep central cavity reaching 

 far towards the root, and near the base pad-like or nodular 

 excrescences, separated by depressions, at Avhich the wall is 

 often broken through. Surface with numerous irregularly 

 scattered circular or oval ostia of various sizes, from which 

 simple radial canals pass into the wall. Similar horizontal 

 canals commence near the surface, and open into the central 

 cavity. Skeleton of regular quadriradiate corpuscles of con- 

 siderable size, having the four main arms smooth and round, 

 and their ends divided into several branches with short root- 

 like processes. In well-preserved specimens the surface has 

 a coat of elegant forked anchors ; and among the corpuscles 

 there are numerous uniaxial pointed or blunt spicules of 

 various sizes. 



Some species have a cylindrical stalk, 50-80 milHms. in 

 length, on which there are no ostia, but which contains ver- 

 tical tubes and has a quite different microstructure. To the 

 naked eye the stalk appears composed of long somewhat 

 curved fibres parallel to the long axis. Under the microscope 

 these fibres are shown to be long, distorted, Lithistid corpus- 

 cles, one ray being enlarged at the expense of the others, 

 which are reduced to small lateral branches, which become 

 weaker and weaker below. In the upper part of the stalk 

 there are, between the fibres, small, indistinctly quadriradiate, 

 strongly ramified, Lithistid corpuscles. All the species are 

 from the Upper Cretaceous. 



