304 ORTMANN—CORRELATION OF SHAPE AND 
while D. dromas caperatus is the compressed form, with the di- 
ameter less than 50 per cent., and without hump. But we must bear 
in mind that some moderately swollen individuals have no hump; 
and that, more frequently, flat specimens may have more or less 
distinct traces of this hump. 
The original measurements taken from Lea, Conrad, and Simp- 
son, give for the typical form a diameter ranging from 50 to 84 per 
cent., while the diameter of caperatus ranges from 42 to 48 per cent. 
I am able to submit the. following table. 
Loc. No. Max. Min. Av. 
Tennessee River. ' 
SRMISGUITD Lames sic ee nvaeaievonts ieee 4 74 590 66 drom. 
Keonpcvallen ciicsth. avrertelceiecccueetes I 58 58 58 drom. 
Holston River. 
INCI ETI SAtiog Boeraaauic canoer ne 2 56 53 54.5 drom. 
INTASCO te Meer erect ae cote teen 10 61 43 52 drom. (cap.) 
lSloyclersc: earn etna has acon sorter 3 58 50 55 drom. 
Turley Mill ... me eseecenesecnes G) 63 52 56 drom. 
INO CLO MMe eeeriert ear tva peices Ciel aes I 48 48 48 cap. 
lnlolisiom Stason Levsnoaccooasooc 3 56 47 52 drom. (cap.) 
Farther up in the Holston, this species has not been found. It is 
clear that the form caperatus is not well developed here, and this is 
also shown by the fact that traces of the hump are found to the 
uppermost station, although, on the other hand, already one of the 
specimens at McMillan is without any hump. In the Clinch and 
Powell, conditions are more favorable to the development of the 
caperatus-type, as is seen in the next table. 
Loc. No. Max. Min. Av. 
Clinch River. 
S oliwiaVaerectbare: eicrareare as a¥e chasvaieuarolererers 2 53 49 51 drom. (cap.) 
Bid Semi O Oty esis 0 aeeitetus soe 16 58 4I 49 cap. (drom.) 
Wlinitonmeeees-. uadacosee tiers oe 6 52 43 47 cap. (drom.) 
(OuimDIL Ais eerie Serena Gone op eerisce 5 5I 40 46 cap. (drom.) 
Clinch Raver Statiommss cece eee I 46 46 46 cap. 
Powell River. 
(CombSie paket bee eae Poee I 46 46 46 cap. 
PNM Itoae SA rcredogsrcrs eter seared Make eis Severe I 42 42 42 cap. 
Combs is about equivalent to Clinch River Station. Also here 
the development of the hump is variable, but specimens without it 
