106 



therefore doubtful whether or not it belongs to the genus. Young speci- 

 mens f of an inch in length, and also the smaller extremities of the adult, 

 are destitute of transverse diaphragms. 



This species in its external characters very much resembles Petraia 

 rustica (Billings), Report for 1857, and is found associated with it hi the 

 same beds. The- internal structure at once shows it to be distinct. I 

 referred it to the genus Petraia, and it is figured under that name in the 

 work cited at the head of this description, judging it to be distinct from 

 P. rustica on account of the form of the cup ; but since that part of the 

 work was printed I have had specimens split by a lapidary, and find that 

 it more probably belongs to Zaphrentis. 



Locality and Formation. Drummond Island, Lake Huron. Hudson 

 River group. 



Collector. A. Murray. 



AMPLEXUS CINGULATUS. (N. sp.) 



Description. Corallites very elongate, cylindrical, varying from 3 to 

 8 lines in diameter, annulated at various distances by prominent usually 

 sharp-edged rings of growth, with concave spaces between. Radiating 

 septa from 50 to 80, according to the size of the corallite, extending 

 inwards about one-sixth of the diameter. The inner area occupies full 

 five-sixths of the whole diameter ; the transverse septa or tabulae thin, 

 slightly undulating, from J to of a line apart. Surface with about two 

 longitudinal septal striae in one line, the ridges between which are often 

 divided by a smaller stria. 



The annulations are distant from each other from 2 to 14 lines, the most 

 common distance being about half an inch. They are usually sharp-edged, 

 but often in the younger corallites they are either obtusely rounded or 

 represented by mere enlargements of the diameter of various forms and 

 distances. 



This species appears to be gregarious, as great numbers are found on 

 the same slabs of limestone, lying across each other in all directions and 

 broken into fragments from 1 to 4 inches in length. 



Locality and Formation. Ance a la Barbe, Bay of Chaleurs. Middle 

 Silurian. 



Collector. Sir W. E. Logan. 



