Ukedk.| Carboniferous Invertebrates, 15 



thus exposed in section are very thin, approximately uniform in 

 this respect, and are all perforated with straight, simple, rela- 

 tively large canals. Those traversing the gastral walls (ex- 

 halent pores) are larger than the rest and appear to be of 

 uniform size. The canals perforating the septal (that is, aper- 

 tural) and exterior walls are inhalent pores, and, with this 

 necessary interpretation, the septal cavities may properly be re- 

 garded either as chambers for the accumulation and discharge 

 into the cloaca, or as true ciliary chambers. We find that, for 

 the most part, these skeletal walls have been, perhaps by sec- 

 ondary changes, converted into crystalline calcite, and this 

 change has obliterated the spicular structure, and in some 

 places the perforate structure of the walls. Elsewhere, espe- 

 cially on the external walls, there has often been a deposit of ad- 

 ventitious calcite which, in sections, gives the wall an unusual 

 thickness. It is to be noted that there is no breach in the con- 

 tinuity of the external wall of any given annulation. The septal 

 or enclosed portions of the wall do not meet the outer or exposed 

 part as they meet the gastral wall, but the entire external wall 

 is arched from the peripheral base of the chamber beneath to 

 the apertural margin of the cloaca." Thin vesicular tissue 

 often extends from the gastral to the dermal wall and some- 

 times between each other. 



Range and distribution : Upper Coal Measures ; Thayer, 

 Topeka. 



I have a single specimen of this species from the Topeka 

 limestone. It agrees very well in all respects with the speci- 

 mens figured by Clarke. The smaller end was broken away 

 before fossilization, making it appear to have the aperture at 

 the smaller end of the specimen, and the septa sag downward in- 

 stead of curve upward. There are several specimens probably 

 of this species from Thayer, which are too poorly preserved in- 

 teriorly to determine specifically, but the exterior resembles 

 very much this species, to which it is referred. Associated 

 with the above, at Thayer, is a smaller variety, very much more 

 constricted at the juncture of the septa and the outer wall, giv- 

 ing it very much the appearance of a row of large beads set 



