QUADRULA gII 
Lea received the only specimen I have seen, the type from 
Wheatley, who had labeled it Unio psoricus. It differs most 
decidedly from that species, being longer, more inflated, dif- 
ferent colored, and having much deeper beak cavities. This 
species was overlooked by accident when making up the Syn- 
opsis. 
QUADRULA QUADRATA 0. S. 
Shell subquadrate, subcompressed to convex, rather solid; 
beaks located subcentrally or near the anterior end, rather high 
but compressed and turned inward and forward; posterior 
ridge rather low, wide and double; posterior end subtruncated ; 
base slightly incurved behind; surface covered with small pus- 
tules and irregular, low, concentric ridges; epidermis dirty 
brown, in places tinted with bottle-green, decorticated on the 
nodules ; left valve with two strong, low, ragged, radial pseudo- 
cardinals with an imperfect, much torn tooth between and two 
small laterals; right valve with one ragged pseudocardinal 
and one lateral, partly divided ; beak cavities deep, compressed ; 
anterior scars rough; pallial line distant from the shell border ; 
nacre creamy-white. 
Length 67, height 55, diam. 33 mm. 
Length 72, height 53, diam. 27 mm. 
Length 60, height 50, diam. 30 mm. 
Usumacinta River, Guatemala. 
The National Museum possesses three specimens sent by 
Dr. von Ihering from the above locality, which I at first doubt- 
fully considered to be the Unio ostreatus of Morelet and one 
of them has something of the outline of that species. In gen- 
eral it is much more quadrate, it is a smaller and more delicate, 
more compressed species and the pseudocardinals are very 
different. Those of quadrata are low and rather wide, while 
in ostreata they are high and subcompressed. The National 
Museum recently received a fine series of ostreata from 
Messrs. Nelson and Goldman, collected in southern Mexico, 
and the difference in the two species is at once apparent. 
