1 6 LOWER PENINSULA. 



group of Point Detour and Drummond's Island, Exteriorly it 

 fully resembles Heliolites interstinctus. 



Plate III. — Fig. i represents a silicified specimen from Point De- 

 tour, Lake Huron. 



LYELLIA PARVITUBA, Nov. Spec. 



Tubes one millimeter wide, with projecting orificial rims, radi- 

 ated within by prominent spinulose crests, and on the surface 

 of the interstices by the converging arrangement of the coenen- 

 chym vesicles. Interstitial spaces about equal to a tube di- 

 ameter, vesicles rather coarse. Diaphragms subplane, granulose. 

 Growth explanate, discoid, with a concentrically wrinkled epi- 

 theca on the lower side. Rarely found in the Niagara group of 

 Drummond's Island. In the Niagara group of Indiana and Ken- 

 tucky this species is very common, and is partly found silicified, 

 partly in calcified specimens with finely preserved structure. 



Plate II. — Fig. 4 is a calcified specimen from Louisville, Ky. 



Various other forms described by Billings under the name of 

 Heliolites are by structure true Lyellias, as Heliolites affinis, Bil- 

 lings ; Heliolites speciosus, Billings ; Heliolites exigiius, Billings : all 

 found at Anticosti Island. 



HOUGHTONIA. 



N. Gen. 



Tubes circular, with projecting rims ; cavity lined by twenty 

 or more longitudinal crests, and transversely septate by subplane 

 diaphragms. Coenenchym formed of irregularly lacunose cell spaces 

 anastomosing amongst themselves, and frequently by pores with 

 the tube channels. Intertubular interstices narrow — the tubes are 

 often in immediate contiguity, so that the intertubular coenenchym 

 becomes restricted to the corners left between the joining tubes. 

 No pore communication between the contiguous tube walls. 



