no. 1823. AIOLLUSKS OF THE GENUS CERITHIOPSIS— BARTSCH. 331 



Basal keel obsolete. 



Axial ribs retractive antemunda. 



Axial ribs protractive diomedese. 



Shell very slender galapagensis. 



Sutures not channeled. 

 Tubercles of middle keel truncated on both posterior and anterior margin. 

 Axial ribs and spiral cords inclosing strong, squarish pits. 

 Base with two strong keels. 



Adult shell more than 5 mm. long alcima. 



Adult shell less than 3 mm. long williamsoni . 



Base with a feeble fasciole only truncata. 



Axial ribs and spiral cords inclosing rounded pits. 



Spiral cords slender cesta. 



Spiral cords very broad. 



Shell very elongate-conic stephensse. 



Shell broadly conic. 



Adult shell less than 6 mm. long stejnegeri. 



Adult shell more than 7 mm. long s. dina. 



Tubercles of middle keel not truncated on both posterior and anterior 

 margin. Tubercles of middle keel truncated on posterior margin only. 



Base marked by a slender fasciole only rowelli. 



Base marked by spiral cords. 



Spiral cords of base three antefilosa. 



Spiral cords of base two neglecta. 



Tubercles of middle keel not truncated. 



Whorls strongly, slopingly shouldered at the summit halia. 



Whorls not slopingly shouldered at the summit. 

 Shell robust. 



Base with a single keel at the periphery diegersis. 



Base with three keels near the periphery montereyensis. 



Shell slender and minute adamsi. 



Spiral cords between the sutures four. 



Shell very large; adult more than 12 mm. long. 



Intercalated cords absent or very fine ingens. 



Shell smaller; adult less than 7 mm. long. 

 Spiral cords wider than the spaces which separate them. 



Shell elongate-conic tumida. 



Shell elongate-ovate peruviana. 



Spiral cords narrower than the spaces which separate them. 



Spiral cords subequal aurea. 



Spiral cords decidedly unequal destrugesi. 



CERITHIOPSIS (CERITHIOPSIS) FATUA, new species. 

 Plate 36, fig. 5. 



Shell very elongate-conic, creamy white. Nuclear whorls three, 

 strongly rounded, separated by well marked sutures, forming a slen- 

 der, regular spire. Post-nuclear whorls well rounded, separated by a 

 deeply channeled suture, ornamented with three nodulose, spiral 

 cords one of which is at the summit, the third immediately above the 

 periphery, while the second is median between the two. These cords 

 are a little wider than the spaces which separate them. In addition 

 to the spiral sculpture, the whorls are marked by retractive, axial 



