1909.] NATURAL SCIENCES OF PHILADELPHIA. 533 



forms are known from southern Mexico. It is an alien in northeastern 



Mexico. 



Xampsilis aztecorum (Phil.). 



Philippi, Abbild., Ill, p. 27, pi. 6, fig. 2. Martens, Biologia, p. 502, pi. 36, 

 figs. 2-4a; pi. 37, figs. 3, 3a,b. 



Zimapan, on the Rio San Juan, a southern confluent of the Panuco 

 (Schiede). Not taken by Mr. Hinkley. 



Lampsilis strebeli (Lea). 



Obs., XII, p. 78, pi. 51, fig. 131; Martens, Biologia, p. 503, pi. 37, figs. 1, 2 

 (as a variety of aztecorum). Nephronaias medellinus Simpson, Synopsis, 

 p. 592, footnote 2. 



Valles River, two miles above Mecos, at the head of the rapids. 

 Taken from crevices in the bed of the stream, where the water was 

 deep and the current so strong that it was difficult to hold one's posi- 

 tion. 



The shells in this place were so badly eroded that a third were 

 discarded. 



This species was described from the State of Vera Cruz. It has 

 been united with medellinus by Mr. Simpson, and with aztecorum by 

 von Martens, but I think it specifically distinct. 



Xampsilis fimbriata Frierson. 



Nautilus, XXI, p. 86, pi. 12, figs. 1-3, Den., 1907. L. salinasensis Simpson, 

 in Dail, Proc. U. S. Nat, Mus., 1908, p. 101, pi. 30, fig. 3. 



Valles River at Valles, at the ranch of Mr. Willis, between Valles and 



Pujal, and two miles above Mecos, where it occurs with L. strebeli. 



"At Valles the water was very shallow, and nearly the whole bed of 



the stream could be waded. The shells were found between and under 



rocks in mid-stream, and a few were taken from a muddy bank across 



the river from the town." This fine Lampsilis is related to L. strebeli 



on the one side, to L. discus on the other. 



Lampsilis discus (Lea). 



Unio discus Lea, Obs., II, p. 74; III, p. 72. Von Martens, Biologia, p. 509, 



with var. connectens and panucoensis, p. 510. 

 Unio lapidosus Villa in Kobelt. 



Moctezuma River. "Just below the ford the river is divided by a 

 large island. The stream on the right has a strong current; that on 

 the left is checked to some extent by a rock outcrop at the lower end 

 of the island. In this part of the stream quite a bed of this species 

 was found." (A. A. H.) 



The type locality is the Rio Moctezuma. The varieties described 

 by Prof, von Martens cannot be sustained. They occur together 

 and fully intergrade. It is a magnificent species, one of the largest 

 in Lampsilis. The nacre may be white, salmon or purple. 



