634 



MEMOIRS OF THE CARNEGIE MUSEUM. 



other specimens are in the Carnegie Museum, without exact locahties, from the 

 HoUand and Juny collection respectively. 



Distribution. — Restricted to eastern Brazil, to the drainages of the Rio Parana 

 in Sao Paulo, and of the Rio Paraguassu and Rio Sao Francisco in Bahia and 

 Sergipe. Possibly more widely distributed in the Sao Francisco system. 



Haas (1916, p. 37, 58) gives this species also from Rio Unuyacu (tributarv 

 to Rio Napo) in Ecuador; however, he conceived it in Simpson's sense, and we 

 cannot be sure that it is M. siliquosa as defined by Von Ihering. 



Mjr specimens fully agree with the account given b}' \'on Ihering, and their 

 measurements come verj' close to those given bj^ him. 



Measurements. 



The figures for Spix' type are taken from Von Ihering (1890). Von Ihering 

 (1910, in the key) gives the location of the beaks as ranging from 18 to 29 pr. ct. 

 and the height as ranging from 35 to 37 pr. ct. of the length. 



Remarks. — In all of my specimens, the posterior adductor scar is presinual. 

 M. bahia is founded upon a single specimen, which has the measurements: L. 78, 

 H. 27 = 35 pr. ct., D. 15.5 = 20 pr. ct., beaks at 23 = 30 pr. ct. These figures 

 fall within the range of variation of M. siliquosa. In Von Ihering's key there is 

 here a w'eak point, since the forms are distinguished chiefly by the location of the 

 beaks, with the figures partly overlapping. I cannot find any difference in bahia 

 from siliquosa, except that the lower margin in the former ascends slightly behind, 

 and that the posterior adductor scar is said to be "subsinual, in part even a little 

 presinual." The first character very well may be individual; the second, dis- 

 regarding the fact that it is hard to understand, does not at all differ from siliquosa, 

 where this scar is simj)ly presinual. Indeed, my young specimen from Lagoa 

 Salgado has the adductor-scar less in advance of the ligamental sinus than the 

 larger. Altogether, this young specimen is extremely close to bahia, only the 

 posterior lower margin is not curved up, and the beaks are more anterior. It is 

 also remarkable for the great thinness and transparency of the shell. Therefore 

 I think that M. bahia is only a 3'oung individual of M. siliquosa. 



