Palaeontological Speculations.—Gratacap. 291 
In Dr. Beecher’s striking and memorable contribution the 
“Development of the Brachiopoda” (A. J., Vol. XLL., p. 343, 
Won SLuLV., p. 133) we are shown a series of connected 
changes extending over a vast period of time, presumably un- 
der very varying conditions, quite undeviatingly continued 
until a structural limit has been reached. He has emphasized 
the progressive dissimilarity in the form and relation of thie 
valves of Lingula, Terebratulina, Cistella, Discinisca, Theci- 
dium and Crania; he shows us that these variations are related 
to two important organic characters, viz.: “the length and di- 
rection of the pedicle and the position and structure of the 
pedicle opening.” He has drawn attention to the “types of 
pedicle openings” and as they “furnish a method for an or- 
dinal grouping of the genera of brachiopods”’ it is significant 
that “this is found to agree with the chronological history of 
the class.” 
Take again the orderly and consecutive movement of parts 
from a larval or primitive state to a fixed, mature condition, 
which Beecher has discussed in his “Classification of the Tril- 
obites.” (Amer. Jour., 4th Series, Vol. III.). The eyes in the 
first stages of trilobitic evolution have been ventral presum- 
ably, and they have in the higher or later forms migrated to 
the dorsal position. So Dr. Beecher gives the progression of 
these characters in the following steps: (1) absence of eyes; 
(2) eye lines; (3) eye lines and marginal eyes; (4) marginal 
eyes; (5) submarginal eyes; (6) eyes near the pleura of the 
neck segment. 
Dr. Beecher again points out the changes in the glabella. 
He says (p. 102); “throughout the larval stages, the axis of 
the cranidium shows distinctly by the annulations that it is 
composed of five fused segments, indicating the presence of as 
many paired appendages on the ventral side. In its simplest 
and most primitive state it expands in front, joining and form- 
ing the anterior margin of the head (larval Ptychoparia and 
Sao). During later growth, it becomes rounded in front, and 
terminates within the margin. In higher genera, through ac- 
celeration, it is rounded and well defined in front, even in the 
earliest stages, and often ends within the margin (larval Triar- 
thrus and Acidaspis). From these simple types of simple pen- 
tameous glabellz, all the diverse forms among species of var- 
