2 PBOCEEDINGS OF THE XATIONAL MUSEUM. vol. G6 



where it remains but has curled away from the ray in the shelly 

 substance. 



The two chief facts which have been discovered in the Corbiculidae 

 since the time at which these mollusks were segregated into a family 

 by themselves lie in a discovery made by Prime and a later one made 

 by Dall. Prime's discovery is given in the following sentence quoted 

 from his Monograph of American Corbiculadae (Recent and fossil).^ 

 "A peculiarity of the Corhicula found in America, which they share 

 with our Cyrena^ lies in the fact that the pallia! impression always 

 terminates in a sinus, whereas in the species from other regions it 

 is simple." 



Dall discovered the fact that Corhicula Ihnosa and C. ohsoleta are 

 viviparous. See his Note on Neocorhicnla Fischer.^ 



Two specimens from Doctor Felippone from Colonia, Uruguay, 

 contain nepionic young, thus proving anew that at least some of the 

 species are viviparous as pointed out by Dall. 



Both shells are quite small, showing that breeding begins at an 

 early stage. One, at least, is positively Corhicvla limosa. This spec- 

 imen measures 11 mm. in length and 9 mm. in height. It contains 

 embryos from the Qgg up to shells of a considerable size, giving one 

 the idea that the production of young must be somewhat continuous, 

 at least during the breeding season, and that it does not take place in 

 a short space of time. The largest of the young, probably ready 

 for extrusion, measures 2 mm. in length and 1.75 mm. in height. 

 This is a considerable size when compared with the size of the parent. 



The tip of the young shell is transparent, glasslike, and very small. 

 It is prominent like the tip of the genus Mvsculium. A fairly well- 

 marked concentric groove indicates the first period of development. 

 This is followed by several concentric impressed striae and the later 

 portion of the shell has concentric striae resembling on a small scale 

 those of the adult. These little shells are flesh colored, with bright 

 rays of pale chestnut, not evenly distributed, but arranged singly or 

 in pairs or trios. In coloring, the baby shell thus resembles the 

 mother. 



The other specimen mentioned as containing young is of about the 

 same size as the one we have been considering, but it has no rays of 

 color, and it is a little off form for Corhicula limosa. The nepionic 

 young in this specimen resemble the mother in having no rays of 

 color. 



The nepionic young of a specimen of Corhicula ohsoleta in the col- 

 lection of the United States National Museum mimic the mother in 



1 Smiths. Mis. Coll. No. 145, p. 3, Dec. 1863. 



2 The Nautilus, vol. IC, pp. 82, 83, Nov., 1902. 



