378 



in having the pores, in general, one-fourth smaller, and from C Anstedi 

 {ante, pp. 210, 337) in having them larger. 



The above figure, 352, is copied from Roemer, who gives it to illustrate 

 the internal structure of Astylospongia prcemorsa, a fossil sponge which 

 occurs in the Lower Silurian rocks of northern Europe, and also, accord- 

 ing to him, in rocks of the same age in Tennessee.* The structure of 

 the inner wall of the cup is very much the same in both of the species 

 above represented, but still I think they belong to different genera. In 

 our species the walls are as completely reticulated to the depth of six 

 lines, as in the inner surface of the cup itself. This is clearly shown by 

 the fragment above mentioned. There is a great difference also in the 

 general form of the two groups, the species of Calathium being elongate- 

 turbinate like the corals Zaphrentis and Ci/athojyhyUum, while those 

 figured by Dr. Roemer are more nearly globular. The genus Aidoco- 

 pium, also illustrated by iloemer, has some turbinated species, but the 

 figures of the inside of the cup (of which several are given) do not show 

 any perforations : their absence, however, in the figures may be owing to 

 the imperfection of the specimens. 



Locality and Formation. — Mingan Islands ; Chazy limestone. 



Collectors. — J. Richardson, Sir W. E. Logan. 



Genus Receptaculites, Defrance. 



a 



Fig. 353. 



Fig. 353. — Diagram of the structure of Rcceploculites, as it would be shown in a vertical 

 section through a sub-conical species, a, the a;ierture in the summit; 

 b, the endorhin or inner integument lining the central cavity; r, the 

 ectorhin or external integument ; n, the usual position of the nucleus ; 

 V, the great internal cavity. The unshaded bands running from the 

 ectorhin to the endorhin represent the tubes. 



• Dr. Ferdinand Roemer, Die fossile Fauna der Silurischen Diluvial-Geschiebe von 

 Sadewitz bei Oels, in Nieder-Schlemn, p. 10, pi. II, fig. 6. 



