Raymond (46) has pointed out a number of interesting cases of reca- 
pitulation. The very common and well-known Devonian Spirifer, S. mu- 
cronatus, has the cardinal extremities in the adult very acute (mucro- 
nate), sometimes, indeed, drawn out into needle-like points; while the 
number of plications may be thirty or more. In the neanic stage these 
transversely elongated spirifers pass through forms corresponding to the 
adults of certain Niagara species. The adult of S. crispus, corresponds - 
very closely in shape, number of plications, and shell index with these 
young specimens of S. mucronatus. 
Shimer and Grabau (51) have shown that in the upper part of the 
Hamilton series of Thedford, Ontario, there occurs a variety of NSpirifer 
mucronatus, which though not mucronate at all in the adult, is “extremely 
mucronate” in the neanic stage. At this stage also there is evidence of 
the median plication of the sinus, another charactertistic of the adult of 
the normal S. mucronatus. In the adult of the Thedford variety this 
median plication has disappeared. The geological and morphological evi- 
dence of the derivation of this form of S. mucronatus is complete. 
I have pointed out an exactly similar case in the variety senexr of 
Platystrophia acutilirata (16). This variety occurs in the upper part 
of the Whitewater division of the Richmond series of Indiana and Ohio. 
Platystrophia acutilirata, as is well known, is very mucronate in the 
adult, resembling in its general outline, Spirifer mucronatus. It was in 
fact at first referred to the genus Delthyris (Spirifer). The normal form 
is shown by an unusually closely graded series of intermediate forms to 
be descended from P. laticosta, and it repeats the adult characters of the 
latter very faithfully in its late neanic stage, becoming always more mu- 
cronate as development proceeds. The upper Whitewater form, var. 
sener, frequently has entirely lost, in the adult stages, the acute angula- 
tion of the cardinal extremities, so that the lateral and cardinal edges 
make a right, or nearly a right angle. In the young (neanic) stages of 
P. senex, however, the shell is decidedly mucronate, so that these young 
shells exactly resemble the normal Platystrophia acutilirata of the lower 
Whitewater and Liberty formations. P. senex, it may be remarked, is ¢ 
well defined form, and its derivation from P. acutilirata is beyond ques- 
tion, since it is connected with the latter by every gradation. 
Another interesting case of recapitulation among the brachiopods has 
been worked out with great care by Mr. F. C. Greene (27). In this case 
also 10 pains was spared to ascertain the relationships of the various 
