MEGASPIRA. 183 



spiral thread, running on the floor of the cavity of the first 

 half of the last whorl (fig. 2, pi.). 



Length 62, diam. above aperture 11 mm., whorls 23%. 



Length 59, diam. above aperture 10.6 mm., whorls 22%. 



Length 54.5, diam. above aperture 10.3 mm., whorls 22. 



Brazil: Prov. Minas Geraes (Fontaine). 



Megaspira ruschenbergiana Lea, JAY, A Catalogue of Re- 

 cent Shells, edit. 2, p. [81], pi. 1, f. 2 (1836). LEA, Trans. 

 Amer. Philos. Soc., vi, p. 21, pi. 23, f. 101 (June 15, 1838; 

 see Proc. Am. Philos. Soc., i, 1838, p. 19) ; Obs. Genus Unio, 

 ii, p. 21, pi. 23, f. 101 (June, 1838) . SOWERBY, A Concho- 

 logical Manual, p. 63, f. 294 (1839) ; edit. 2, p. 187, f. 294 

 (1842). GRATELOUP, Actes Soc. Linn. Bordeaux, xi, 1839, 

 p. 427, pi. 2, f. 9. M. elatior var. A, KUSTER, Conchyl. Cab., 

 p. 140, pi. 17, f. 5, 7. DESHAYES in Fer., Hist., p. 220. pi. 

 156, f. 1, 2. Balea elatior var. b, PFR., Monogr., ii, p. 390. 

 Pupa elatior Spix, ORBIGNY, Amer. Merid., p. 320. 



This is the largest species of the genus, and the commonest 

 in collections. Dr. Lea gives the measurements of his type 

 as 2.5 inches long, .5 wide, with 23 whorls. It was united 

 with M. elatior by Pfeiffer, and the really important differ- 

 ences between the two species have not before been pointed 

 out. The sculpture is almost exactly the same as in the 

 smaller M. elatior, and the enlarged umbilical cavity and 

 triplicate columella (fig. 4) are like M. elatior robusta; but 

 ruschenbergiana differs from both in the long continuation 

 inward of the subcolumellar lamella (shown in fig. 3, sub.), 

 and in the baso-axial barrier in the back of the penult, whorl, 

 the outer end of which is prolonged in a spiral cord (fig. 2, 

 pi.) on the basal wall. The larger size of the shell, and the 

 more slender axis within the early whorls are further differ- 

 ences. 



There is occasionally a fourth fold, short and tooth-like, 

 on the columella; and in two specimens before me there is a 

 very small, short fold on the parietal wall, standing close to 

 the parietal lamella, on its outer side near the end. 



Fig. 3 represents the interior of three whorls, the third, 

 fourth and fifth from the base, enlarged more than in fig. 2 ; 



