364 MEMOIRS OF THE CARNEGIE MUSEUM 



REMARKS. 



Camharus propiiiquus 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 cliief specific 

 characters, the longitudinal keel of the rostrum, is decidedly variable. All speci- 

 mens at hand from outside of the state (pight) show a keel plainly, l)ut this is not 

 so with the Pennsylvanian specimens. The keel in these is often distinct, Imt shows 

 a tendency to disappear. This is chiefly the case in young individuals, where tlie 

 rostrum is comparatively narrower, the marginal spines are sharper, and the acumen 

 is slenderer than in older individuals. 



The armatu]-e 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 

 tubercle anterior to it, which in young specimens is often spiniforra. 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 Tennsylvanian 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. Put it is remark- 

 able that in the set from ('onneautville 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 increa.se 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 IClk 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 s[)ine 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 IMichigan is remarkable for the fact 



