STATION IN FRESH-WATER MUSSELS. 283 
sents, in the more obese form, distinctly the shell called by Lea 
trigonus, and thus I shall use this name, and restrict myself to the 
two forms flava and trigona, and their interrelation, leaving the 
decision as to the standing of wndata to further investigation. Ac- 
cording to Utterback,’® the latter also passes into trigona, 
Loc. No. Max. Min. Av. 
Ohio River. 
Coraopolistesmce erase Se oats 14 63 49 54 flav. (trig.) 
Monongahela River. 
IEGI Zl CLIP average seamete sey oro lseeusiae os /otoke I 49 49 49 flav. 
(ClagWel cont eee eae ore eee 8 66 50 56 trig. ( flav.) 
IMIS ORO Misi aaceucteyete’<rsisrels,norers 41 eres o I 47 47 47 flav. 
The following are tributaries going into the Monongahela at and 
above Millsboro. 
Loe. No. Max. Min. Av. 
N. Fork Ten Mile Creek, Amity.. 2 48 48 48 flav. 
S. Fk. Ten Mile Cr., Waynesburg 6 48 4I 44 flav. 
Dunkard Creek, Wiley .......... 2 47 43 45 flav. 
Dunkard Creek, Mt. Morris ..... 10 50 AI 47 flav. 
The law is again apparent here: the most compressed forms are 
found in the tributaries, the most swollen ones in the larger river. 
Going up the Allegheny River, and ascending one of its tribu- 
taries, Crooked Creek, the law is not so clearly shown for the reason 
that this form is rare in the Allegheny proper, and is entirely missing 
in the headwaters. Yet indications are seen in Crooked Creek. 
Loc. No. Max. Min. Av. 
Allegheny River. 
(Go dlin evar var ari tereielorsicisican ciole ois B 44 4I 43 flav. 
olime tana snc aalerkae ae ses attasie 2 55 50 53 flav. (trig.) 
Melllliypaenety ete oe te eleva Pttonsue esata a arets 2 42 42 42 flav. 
Crooked Creek. 
VOSStOMigavatencsait erste sckaierovesa.cisiciac ore 29 SI 38 43 flav. 
Sotitlimlsencltamectrcciscrae cisioc suns coe 2 4I 4I 41 flav. 
Grecksidem ers vactee sah toes 8 44 38 41 flav. 
That the compressed form is the one found in smaller streams, 
is also shown by several isolated sets from other tributaries of the 
Ohio, which have been measured, and the following are of interest. 
13 dmer. Midland Naturalist (Notre Dame, Ind.), 4, ’16, p. 21. 
