104 ROYAL SOCIETY OF CANADA 
be regarded as running through the Coldbrook and Lower Etchemin 
Faunas, and to have increased four fold in that time; or, if one should 
omit the Coldbrook species, they doubled in size. 
The series of Oboli as a whole increased eight fold; but the two 
species of the Upper Etcheminian are of a different phylum, one 
especially, O. Bretonensis, was separate, if one may judge by the unusual 
course of the vascular trunks of the ventral valve, which, for an Obolus, 
are very close together. The two species of this fauna (O. lens and 
O. Bretonensis) have a similar sculpture, and are likely to be from 
the same root form. 
As a result of this enquiry one may present the following con- 





densed statement: 
Number of integers 
NAME OF THE GENUS OR PHYLUM FROM of increase of 
Range in Time. bulk of the latest 
WHICH THE FORMS HAVE SPRUNG species beyond 
the first. 
Entire Cambrian ..| Acrotreta, earliest species. A. papillata prima 3°2 
Basal Cambrian ...| Leptobolus, ‘ + Htorrentis 70" 2°5 
Includes Lower 
Etchemin........ Lingulepis, ‘“ a Ibs MCW ease caoe SG) 
Same, or for 4'3rate 
Basal Cambrian..| Lingulella, ‘“‘ à L. cf. longovalis .. 4°3 or 1'5 
Lower Etchemin 
inclusive......... Obolus, ve S Os torrentis.. 2... 4°4 
Basal Cambrian as 
a whole........ .| Obolus, as a genus, based on form........... 8:5 
ACROTHYRA. 
As a contrast to this result we present the variations traceable 
in the genus Acrothyra, from its earliest known appearance to the 
latest form, of which we have positive knowledge. This covers the 
whole of the Basal Cambrian time. 
SIZE OF VENTRAL VALVES OF ACROTHYRA FROM THEIR FIRST APPEARANCE 
TO THE TOP OF THE BASAL CAMBRIAN. 








Selo ena nee 
Assise NAME | Ce an eet gt AE 
vo Es o ge a 
4 F A oy x 
mm | mom mm 
Co : A. signata-prima....... Ske Rei at ir Se Er 24 24 1} 6°25 
E. 1b A sionata (YPO) oser 3 2 1 2 6° 
E.1le AUN Se, Cee SOA et oa Ree oe ae bone 24 24 14 1"72186:25 
E. 14 AOS, eR cents Las EA ae NR and) SCI 24 3 14 2 00\NT eo 
E. 2¢ AL ttenter OLGA a ore SAS oe 2 12 14 12 | 3:5 
E.3a A. proavia-prima....... ..... Od ete 3 2 2 ees 
E. 3 e BALM tte CLASSE MS Hele dee eins, sia¢ 24 2 13 12311167 
E.3e A \proavia (EYpe)--2-t2 4h otre marie 3 2 14 1°3 | 6° 
Increase of the latest beyond the first....|......|......|.. ...|...... “95 
