326 CRUISE OF THE NEPTUNE 



Halysites catenularia, L. 



Represented by a small corallum, round which has grown 

 a stromatopora. This coral exhibits the structure characteristic of 

 the typical form of the Niagara formation, viz>, moderate sized cor- 

 allites, oval in transverse section with narrow tubules intervening. 

 Four corallites are included in a space of 8 mm. 



This form also occiTrs in the Guelph limestone of Ontario. 



A second and particularly interesting specimen was obtained 

 by Mr. Low at Southampton island. It differs from the typical form 

 in having corallites of noticeably large size, and agrees in this par- 

 ticular with a specimen from the Guelph limestone at Durham, Ont. 

 (J. Townsend, 1884), in the museum of the Survey. The Durham 

 fossil has not the finer details of structure sufficiently well preserved 

 to show the minute tabulae of the tubules, but in Mr. Low's specimen 

 longitudinal sections of the tubules clearly reveal the highly arched, 

 close set tabulae within. There are three corallites in a space of 12 

 mm., as in the Durham specimen, and the tubules have a width of 

 about '75 mm. 



Plasmopora follis, M.-E. and H. 



To this species is referred a small specimen showing the inner 

 structure fairly well. The corallites vary in diameter from slightly 

 under to a little over 1 mm., and they are mostly less than their own 

 diameter apart with from one to three tubules, in the shortest line, 

 between neighbouring corallites. This species is generally considered 

 to be typical of the Niagara group. 



Pycnostylus elegans, Whiteaves. 



A few specimens weathered so as to show only the inside of the 

 corallites which vary in diameter from 7 to 15 mm. An interesting 

 feature of these specimens is the preservation of the free edges of the 

 septa which are seen to be denticulated, about seven denticles occur- 

 ring in a space of 2 mm. A re-examination of the type material re- 

 veals the presence of these denticles, although they are poorly pre- 

 served. Mr. Low's specimens are referable to the species from the 

 Guelph limestone of Ontario with large corallites (from 13 to 17 

 mm. in diameter) as in the other and type species from the same 



