24 SPIRAXIS. 



18. S. NITIDUS Strebel. Vol. I, p. 52. 



Var. major Martens, pi. 2, fig. 14. Length 10 to 11.5, diam. 

 2.5, aperture 2x1 mm., 9 to 10 whorls. Las Vigas (Hoge). 

 The type is probably immature. 



Var. minor Martens. 5.66 x 1.33 mm., with 814 whorls. 

 Pacho, Canino de Obispo and Mirador (Strebel). 



Var. pittieri Martens, pi. 2, fig. 15. More elongate, smooth, 

 with 10 whorls, the apex globose, very -obtuse. Length 10, 

 diam. 2, aperture 1.66 x 1.25 mm. El Pital and Savana de 

 Guacimo, in S. W. Costa Rica (Pittier). Probably a dis- 

 tinct species. 



19. S. TAMPICOENSIS Pilsbry, n. sp. PI. 20, fig. 1. 



The shell is long and very slender, acicular, corneous- 

 whitish, thin, composed of T 1 /^ whorls, which are strongly 

 flattened, but separated by a deep suture. The summit is 

 very obtuse; first 2~y 2 or 3 whorls are nearly smooth; then 

 riblets weakly appear, gradually becoming stronger, until 

 on the later 2 or 3 whorls they are conspicuous, very oblique 

 and nearly straight ribs, parted by weakly, finely striatulate 

 spaces two or three times their width. There are also, in the 

 largest examples, a narrow varix or two, larger than the ribs. 

 The aperture is very oblique, oblong, broadly rounded basaMy. 

 The outer lip is narrowly expanded, very strongly arcuate 

 near the upper insertion, where it runs horizontally. The 

 columella is broadly concave below, entering in a low fold 

 above. The internal axis has a low spiral prominence run- 

 ning nearly to the summit. Length 3.9, diam. .85 mm. 



Tampico, northeastern Mexico, in river debris. (A. A. 

 Hinkley). 



This is quite unlike any form of Spiraxis or Pscudosiil)- 

 ulina known to me, by its very oblique sculpture and aperture, 

 the horizontal insertion of the outer lip, which moreover is 

 noticeably expanded, and by the very marrow contour of the 

 whole shell. Its generic position is somewhat uncertain. 



20. S. COSTATOSTRIATUS (Pfeiffer). 



Shell imperforate, turrite, thin, closely striate and having 



