58 THE CHICAGO ACADEMY OF SCIENCES. 
cent, confluent ; posterior adductor muscle scar wide, not much 
impressed, confluent, iridescent; protractor pedis muscle scar 
wider than long, not muchimpressed ; dorsal muscle scars situ- 
ated on the posterior face of the cardinal teeth, pit-like; pallial 
line slightly impressed in the anterior part of the shell; cavity 
of the beaks shallow; nacre silvery bluish white, iridescent, 
salmon tinted toward the beaks, In old specimens the interior 
of the valve is bordered by a wide band (6-8 mill.) of dark pur- 
ple or violet. 
Length, 104.00; height, 57.00; width, 27.00; mill. ¢ (9333). 
i) 951.0:00; SN OROO O's 5 88:00;! | “=~ 2 {abel 
‘162.00;  B1,005<- ** 46.00; “* Gi(eoll. fensen): 
Animal: Generally flesh colored or salmon, inclining to yel- 
lowish brown in places, yellowish white on abdomen and black 
on tentacular part of siphons; ctenidia short and wide, the 
inner one the largest, rounded before and pointed behind, united 
to each other and to the opposite pair for their entire length, the 
outer filled throughout with embryos in the female; labial palpi 
not large, rounded—triangular, united and attached at base and 
partly above; siphons yellowish white inside, shading into 
brownish and jet black on the edge of the tentacular portion, 
the tentacles being short; foot thin, dark flesh color; liver 
brownish, tinged with yellow; mantleratherthin. Heart pulsa- 
tions slow and regular—thirteen per minute. 
Distribution: Southern Canada south to Texas and Ala- 
bama, New England west to Kansas. 
Geological distribution: Pleistocene. 
Habitat; About the same as 4. complanata. 
Remarks: A species at once distinguished by its rugose 
posterior margin. A. fressa Lea has a general resemblance, 
and is frequently confounded with the present species by many 
conchologists, but the character of the umbones will at once 
distinguish the two species. See remarks under fressa. A. 
rugosa seems to be an abundant shell and is a lover of muddy 
rivers, at least in this region. It is found in great variety of 
form and size in Thorn Creek and the Little Calumet River. 
Specimens from the former locality. are very rugose. 
GROUP OF ALASMODONTA PRESSA. 
5. Alasmodonta pressa Lea, pl. vi., fig. 3; pl. x., fig. 4. 
Unio pressus LEA, Proc. Amer. Phil. Soc., Vol. II., p. 237, 1843. 
Symphynota compressa Lea, Trans. Amer. Phil. Soc., Vol. III., p. 450, 
pl. xii., fig. 22, 1830. (Preoccupied.) 
Ee 
