546 MEMOIRS OF THE CARNEGIE MUSEUM. 



said to be bottle-green, almost black posteriorly, in nocturnus. I do not think that 

 this is sufficient to sejiarate nocturnus from paranent^ift, since in the latter olive- 

 green tints may also be noticed. This is seen chiefly in a si^ecimen from the Hart- 

 man collection, without locality, preserved in the Carnegie Museum. Moreover, 

 the original descrij^tion of Lea's paranensis mentions this color. 



The variability of the beak-sculjjture of this species is remarkable. It has 

 never been described in detail, except that it consists of rather heavy radial bars. 

 In most of my specimens these bars are rather short (hardly more than 15 mm. 

 long), but in three (all isolated valves, two from Asuncion, one young from Corum- 

 ba) it extends farther, 25 to 27 mm., and chiefly in the young one (PL XXXIX, 

 f. 7) this is very striking, since in this case the beak-sculpture extends over nearly 

 half of the shell. I see, however, no other difference in these specimens, and even 

 among them the bars are not uniform in length. I believe that U. paraguayanus 

 Von Martens is founded upon such specimens. The dimensions of this fall easily 

 within the range of variation of paranensis. According to Von Martens they are: 

 length 102 mm.; height 82 mm. = 80 pr. ct. of length; diameter 47 mm. = 46per. ct. 

 of length. The location of the beaks is given as " three-fourths of the length," which 

 jirobably corresponds to 25 pr. ct. of length, we measuring from the anterior ex- 

 tremity, the author having reversed the procedure. 



Von Martens comjiares his species with nocturnus, but says that it is larger, 

 with stronger sculpture (meaning apparently the beak-sculpture), and larger 

 hinge-teeth, but all these characters are unreliable, and do not distinguish it from 

 pai'anensis. 



Anatomy. — The soft parts of two males and three barren females from San 

 Isidro are at hand. 



Color whitish, distal part of foot gray. 



Anal opening closed above ; the closed part being two to three times as long as 

 the open, which is slit-like, and shorter than the branchial opening. Anal and 

 branchial separated by a solid mantle-connection. Branchial opening with small, 

 but distinct, ]iapill8e. Paljii subtriangular, lower margins curved, jiosterior margins 

 connected for about one-third of their length. 



Gills moderately wide, posteriorly of about the same width, but anteriorly 

 the inner gill is much wider. The shape of the latter is subtrapezoidal, that of 

 the outer gill subtriangular. Anterior end of outer gill near the highest point of 

 the mantle-attachment-line, that of the inner gill immediately behind the palpi. 

 Inner lamina of inner gill entirely connected with abdominal sac. 



Structure of non-marsupial gills as usual, with few and scattered interlaminar 



