112 Anniversary Address to the 
in the main sound and near to the truth, it becomes an in- 
quiry of considerable interest to ascertain how far the ranges 
of these genera are continuous in time; in other words, 
whether the theory of unique generic time-areas be borne 
out among the Brachiopoda, now that we may be said to have 
attained so extensive a knowledge of their generic and specific 
types. This was doubtless the idea working in the mind of 
Von Buch, when, with indifferent materials, he attempted to 
fix the characters of the fossil Brachiopoda, and plainly has 
often influenced the numerous attempts at their classification 
made by subsequent paleontologists. I have no reason to 
suppose that an a@ priori hypothesis, connected with either 
time or space-distribution, influenced Mr Davidson in com- 
ing to his final arrangement, and therefore I have been the 
more curious to see how far that arrangement accorded with 
geological considerations. 
In the first family, Terebratulide, the typical genus Tere- 
bratula (of which Terebratulina and Waldheimia are re- 
garded as subgenera), the succession of types is continuous 
from the middle paleozoic or Devonian epoch to the present 
time ; whilst the other genera are either Upper Mesozoic, 
Tertiary, and recent (as Terebratella and Argiope), ex- 
clusively Upper Mesozoic (as Magas), or exclusively recent 
(as Bouchardia, Kraussia, and Morrisia.) 
Stringocephalus follows as the type of a provisional family, 
exclusively Devonian. | 
The Thecidide, represented by Thecidium alone, range 
continuously from the Trias to the present time. 
The Spiriferide concentrate towards the paleozoic pole. 
In this family Mr Davidson includes Spirifer (with Spiri- 
ferina and Cyrtia as sections), Athyris, Spirigera, Uncites 
and Atrypa. | 
Rhynchonella, with Camerophoria and Pentamerus, form 
a family under the name of Rhynchonellide. The absence 
of perforations in the shell is the rule in this group. The 
typical genus is one of the links between the paleeozoic and 
present epoch, and has its maximum in the Mesozoic. 
The Strophomenide, Productide, and Calceolide all con- 
centrate in the Paleozoics ; Leptena only, in the first named 
family, extending into the lower Jurassic strata. 
OO I EE wad eT 
