562 MEMOIRS OF THE CARNEGIE MUSEUM. 



Several other specimens arc i)rcscrved in tlie Carnegie Museum, from tlie 

 Hartman, Smith, and Juny collections, but all are labelled "Amazon River." 



Distribution. — According to Simpson Eastern Peru to Guiana; south through- 

 out Brazil. However, the few special localities known arc all on the Amazon and 

 its tributaries. 



It should be remarked in the first place that all my specimens undoubtedly 

 represent but one species, showing a great deal of variation, the various forms all 

 connected by intergrades. 



Simjison describes this species as having a "subrhomboidal" shape and with 

 the beak-sculpture covering only part of the surface. He retains H. transversa 

 Hupe (from Brazil) as a distinct species, which has "rhomboidal" shape, and only 

 a "few strong umbonal ridges." Specimens from the Rio Tapajos at hand repre- 

 sent both forms, and pass gradually into each other, so that I am forced to regard 

 H. transversa as only an individual variation of H. corrugata. 



The extreme development of the l^eak-sculpture, covering the whole shell, 

 is found in H. rugosissima Sowerby. Some of my specimens apjiroach this con- 

 dition, but none fully agree with Sowerby's figure (XVH, Hyria, 1869, PL 3, fig. 5), 

 so that this form is not represented in my material, and I cannot say whether it 

 is a good species or not. 



Sowerby (/. c, PI. 2, fig. 3) distinguishes H. exasperata (British Guyana) from 

 H. corrugata (PL 1, fig. 1), the former being longer and more compressed, the latter 

 shorter and more swollen. Simpson unites these two; but among my material I 

 have no specimens which corresponds exactly to the corrugata of Sowerby. If the 

 two should be different, my specimens would fall under exasperata Sowerby (1869) 

 which undoubtedly is synonymous with Triplodon rugosum Spix (1829). 



Frierson (1915, p. 363) has recently described H. amazonia. In outline this 

 easily falls within the range of my specimens of corrugata, chiefly specimens with 

 less developed beak-sculpture (H. transversa Hupe). But H. amazonia is decidedly 

 more swollen. Being founded upon a single specimen, it is impossible to decide 

 whether amazonia is a good species. 



In shape my specimens vary greatly. They are all rather compressed, but 

 there is some variation in this respect. The greatest irregularity, however, is seen 

 in the outline and beak-sculpture. The wings of the shell are of various sizes, 

 chiefly the posterior one, which may be rather short, or drawn out, broader or 

 narrower, and may be more or less elevated. Sometimes the wings assume freakish 

 shapes, curving up or down, or being deflected laterafly. Thus the whole shell 

 is mor(> or less elongated, and more broadly or more narrowly triangular. The 



