PALA£ONTOLOGT. 1 1 



found, in which, by incrustation of the wall substance, the tube 

 channels are narrowed, and the contrast between the larger and 

 smaller tubes is diminished ; these have a spongious aspect, and ap- 

 pear at first glance to be a fossil of totally different structure from 

 the more regularly formed specimens. It is sometimes dif^cult to 

 distinguish this species from the next described species, Hcliolitcs 

 intcrstinctus. This species is found in association with the former 

 kind at Drummond's Island, and in the other mentioned localities 

 in Michigan ; it is likewise common in the drift. The Niagara 

 group of Iowa and Wisconsin incloses the same form. 



Plate I. — Fig. 2 represents two specimens from Drummond's 

 Island, in natural size. 



HELIOLITES INTERSTINCTUS, Linn. 



Visceral tubes from one to one and a half millimeter in width. 

 Vertical crests quite prominent, almost reaching the centre, and 

 composed of rows of spinules pointing obliquely upward with their 

 apices. Coenenchym composed of minute, polygonal, transversely 

 septate tubules. Interstitial spaces between the larger tubes usu- 

 ally much exceeding one tube diameter. Diaphragms rarely flat, 

 and simple, generally complicated into a cellulose network with the 

 spinulose, vertical crests, with a nodular projection in the centre, 

 formed by the converging apices of the spinules. No central col- 

 umella. In vertical sections the channels of the larger tubes are 

 scarcely distinguishable from the surrounding septate ccenenchym, 

 because the intersection of the spinules with the diaphragms divides 

 the interior of the larger tubes into small cell spaces similar to the 

 surrounding coenenchym tissue. The visceral tubes always resist. 

 decay better than the coenenchym, and are preserved as slender, 

 longitudinally carinated columns, held together by a portion of un- 

 destroyed ccenenchym. The mode of growth is in discoid, subplane 

 expansions, with a concentrically wrinkled epithecal crust on the. 

 lower side. 



It is of rare occurrence in Michigan ; occasionally specimens 

 are found in the drift of the Lower Peninsula, but it is a very com- 

 mon species in the Niagara group of Indiana, Kentucky, Tennessee, 

 etc. 



Plate I. — Fig. i is a specimen from Louisville, Ky., in calcified 



