29 



Cumings and Galloway {op. cit.) describe the species Stigmatella sessilis 

 in the following terms: — 



Zoarium discoidal about 15 mm. in diameter and three millimetres thick in the centre, 

 growing parasitically upon foreign objects. There is no basal epitheca. 



The zooecia as shown by tangential sections, are polygonal, their apertures oval or circular, 

 10 zooecia in two millimetres. Surrounding the aperture is a ring of very light coloured schle- 

 renchyma, which is in turn surrounded by a very thin dark ring. The median line is usually 

 light in colour, but is absent in some places, in which case the two dark rings constitute the median 

 line. Mesopores are practically absent. Acanthopores are numerous, 10 in 10 zooecia, quite 

 constant in size about 2/3 the size of number 1, that is 1/30 mm. in diameter. The lumen is clear. 



The zooecia at first are crossed by thin diaphragms, their own diameter or less apart. 

 In this region there is also a considerable number of chain-like mesopores. In the remaining 

 portion of the zooecia the diaphragms are twice their diameter apart. At several successive 

 levels, four in the type specimen, the acanthopores and walls show the characters of maturity, 

 at these levels there is one diaphragm, occasionally two in each tube, at the same height in 

 adjacent zooecia. That these levels represent successive stages of maturity is proven by the 

 specimen, for the growth is interrupted completely in one part of the zoarium at these four levels. 

 This characteristic of rejuvenation and overgrowth is not confined to the genus Stigmatella. 

 It is a common feature of a good many species of Trepostomata and we consider it as an inadequate 

 basis upon which to found a genus. We consider Stigmatella as a valid genus; but we rely chiefly 

 upon the thin walls, small acanthopores, few diaphragms and the presence of mesopores for its 

 recognition. 



The variety Stigmatella sessilis crassa is abundant in the Credit member. 

 It is very similar to S. sessilis in internal characters, but differs decidedly in 

 manner of growth. The variety forms coarse irregular zoaria, tightly adhering 

 to the fragments of other fossils, chiefly the trilobite Isotelus. In some parts, 

 the zoarium is as thin as two millimetres, but in other parts it is very coarse, 

 approaching 20 mm. in thickness. 



Locality. — Credit river, Erindale. 



No. 12172, Royal Ontario Museum of Paleontology. 



Rafinesquina alternata subcircularis, var. nov. 

 Plate VII, Figure 14 



In examining the various specimens of Rafinesquina alternata from the 

 Credit River localities, it was found that they can be separated into two groups. 

 The members of one group resemble the type and are retained under it. The 

 members of the other group differ decidedly from the first and it was decided 

 to give them a new varietal name. 



R. alternata subcircularis is a long form, the length being equal to or slightly 

 greater than the width. The greatest width is not along the hinge line but 

 slightly in front if it, giving a more circular outline to the shell than exists in 

 any previously described form of the species. The shell is very flat; the alterna- 

 tion of the striae is very clearly shown and the median stria is always most 

 prominent. 



R. alternata subcircularis resembles R. alternata fracta (Meek), more than 

 any other form, but it is more circular in outline and without the parallel sides 

 so characteristic of the latter variety. • 



The average width of the specimens is 23 mm. and the height 22 mm. 

 The smallest specimen measures nine millimetres in length, by the same in 

 width, while the largest is 28 mm. long and 32 mm. wide. It is most abundant 

 in the Strophomena varsensis zone in the Erindale member but also occurs in 

 the rocks immediately above the Columnaria reef in the Meadowvale member. 



Locality. — Credit river, Streetsville. 



No. 12173, Royal Ontario Museum of Paleontology. 



