148 MEMOIRS OF THE CARNEGIE MUSEUM. 



Soft parts: As far as studied, identical with those of A. grandis, b,ut gravid 

 females have never been found, and thus the glochidia and the breeding season 

 are unknown. However, the fact that the specimens, collected in May, June, and 

 Juh', were not gravid, indicates that the "interim" falls in these months, as is the 

 case in A. grandis, and thus probably the breeding season will be about the same. 



Remarks: I regard this as a geographical race of A. grandis, which replaces 

 the latter in the St. Lawrence-drainage, and chiefly in the Great Lakes. It is, 

 however, not a "good species," for south of the lakes, and passing somewhat beyond 

 the divide, into the Ohio-drainage, there is a region, where true intergrades are 

 found (in Pennsylvania, Ohio, Indiana, and Illinois). Some of these intergrades, 

 standing nearer to grandis, have been recorded under grandis (see above). And 

 further, even in Lake Erie, the form footiana does not always preserve its typical 

 characters, becoming sometimes more flattened (specimens from the lagoon at 

 Waldamer Park, and from ponds at mouth of Elk Creek, and occasionally else- 

 where), and having heavier beak-sculpture. 



As regards the beak-sculpture, it is essentially of the grandis-type in so far 

 as it consists of four or five (sometimes six) bars, of which the third to the sixth 

 are distinctlj^ double-looped, the loops separated by a sharp, re-entering sinus. 

 Within this sinus the bar is generally lower, sometimes almost effaced, so that it 

 represents a notch, on either side of which the anterior and posterior loop appear 

 elevated. ^°^ However, the posterior loop of footiana, which has the same angular 

 and narrow shape as in grandis, is not so much thickened, and is not so distinctly 

 tuberculiform, and altogether the beak-sculpture is less heavy, finer, and sharper 

 than in grandis. The notch-like shape of the sinus, forming generally an inter- 

 ruption of the bar, shows that this form should be placed under A. grandis, although 

 by the delicacy of the sculpture it distinctly inclines toward A. cataracta. 



In Lake Erie (in Pennsylvania), A. grandis footiana shows two extremes of 

 development of the shape of the shell, which are connected, however, by inter- 

 grades, and are, according to my observations, distinctly dependent on the eco- 

 logical conditions under which they live. 



The most abundant form (among my material) is rather elongated, and closely 

 co'i-responds in the general outhne to Lea's maryattana (Obs. Ill, 1842, PI. 20, 

 fig. 45), but it is not so excessively and abruptly swollen. In its typical develop- 

 ment this form is also characterized by a thin shell, and a peculiar, rusty-brown 

 color, which is especially intense at and near the umbos, passing into brownish 



'™ In some cases, the fifth, and chiefly the sixth bar (if this is present) have the sinus less sharp, 

 resembling only an undulation: this is a variation, which I have never distinctly observed in .1. grandis. 



