318 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
7. Heliolites interstinctus. 
8. Paleofavosites aspera. 
9. Atrypa imbricata var. 
10. Coelospira duboysi (Verneuil). 
11. Dinobolus davidsoni Salter. 
12. Orthis bouchardi Verneuil. 
13: davidsoni Verneuil. 
14. Rhynchonella aprinis Verneuil. 
15. Schuchertella pecten (Linné). 
16. Encrinurus punctatus Wahlenberg. 
17. Proetus cf. distans. Lindstrém. 
18. planedorsatus Schmidt. 
19. Leperditia schmidti Kolm. 
There have also been recognized Clathrodictyon vesiculosum, Favosites 
forbesi, Halysites catenularia, and Pentamerus borealis. 
(b) Borealis banks. This is one of the most remarkable deposits 
of fossil shells I have ever seen. They are almost wholly Pentamerus 
borealis, generally single valves, although in the western outcrops it is 
possible to obtain entire shells. 
Respecting the continuity of this zone it is not possible to speak 
with certainty; but the general facts of the distribution of marine 
organisms would lead to the conclusion that it is not of wide extent 
and it seems very probable that it thins westward. It also appears 
quite probable that in places the character of deposition which gave 
rise to the Jérden beds may have persisted upward while the shell- 
banks grew around, or within such places, that is, the banks are of a 
more or less local distribution. 
The zone makes its first appearance west of Lake Peipus near St. 
Simon’s church, and, narrowing toward the east, the belt of its out- 
crop reaches the coast a few miles south of the city of Hapsal, and finds 
its further continuation on the island of Dago. Schmidt, (Loc. cit., 
1882, p. 526) gives the thickness as forty feet. 
Where the division is typically shown little else is to be seen other 
than myriads of Pentamerus borealis and a few corals. The number 
of the former is simply inconceivable. The rock is wholly a mass of 
the shells, which are chiefly preserved as casts. Where the shells are 
not the dominant component, the rock is either a limestone or a dolo- 
mite. 
About the best locality to see this division, and the one which has 
been selected as the type-locality of the Tamsal formation, is north- 
