364 MEMOIRS OF THE CARNEGIE MUSEUM 
REMARKS. 
Cambarus propinguus in Pennsylvania belongs to Lake Erie and its drainage. 
The range being rather restricted, the material at hand is not very rich, and its 
study does not promise many results as to variation. Nevertheless there are a few 
striking facts, which may be mentioned. In the first place one of the chief specific 
characters, the longitudinal keel of the rostrum, is decidedly variable. All speci- 
mens at hand from outside of the state (eight) show a keel plainly, but this is not 
so with the Pennsylvanian specimens. ‘The keel in these is often distinct, but shows 
a tendency to disappear. This is chiefly the case in young individuals, where the 
rostrum is comparatively narrower, the marginal spines are sharper, and the acumen 
is slenderer than in older individuals. 
The armature of the chelipeds is also rather variable. There is always a strong 
spine in the middle of the inner margin of the carpopodite, and invariably a small 
tubercie anterior to it, which in young specimens is often spiniform. Sometimes 
there is also a small tubercle at the proximal end of the inner margin, but I have 
generally found this only in larger individuals. ‘The lower side of the carpopodite, 
as a rule, has only one spine, located at the articulation with the hand, and this is 
present in all Pennsylvanian specimens I have seen. ‘The anterior margin is often 
without any spine, or even tubercle; there is, however, a low tubercle developed in 
many cases, and in two cases it was spiniform, viz., in a male (second form) from 
Elk Creek, Miles Grove, and in a female from Presque Isle. Both of them had a 
distinct keel on the rostrum, so that they undoubtedly belong to this species. The 
rows of spines on the lower margin of the meropodite are generally represented by 
only two spines, the distal spine of each row being alone present. But it is remark- 
able that in the set from Conneautville Station, composed of twelve individuals, ten 
show an increase of the spines of the inner margin, from four to eight little teeth 
being present behind the large distal spine, while in eight specimens an additional 
smaller spine is found behind the distal spine of the outer margin. In every case 
this occurs only on one side, while the other side is normal. A similar increase of 
the number of spines of the meropodite is also to be observed in a few specimens 
from Temple Creek, Albion, in the two specimens at hand from Elk Creek, Miles 
Grove, in the female from Presque Isle, mentioned above, and in the specimen 
(female) from Sandusky, Ohio. Since the latter has also a spine on the anterior 
margin of the lower side of the carpopodite, the tendency to develop additional 
spines may extend simultaneously to carpopodite and meropodite. 
The set of seven specimens from northern Michigan is remarkable for the fact 
