MAZATLAN TTJTIVALVES 303 



arcuatis ornatis ; decumbente, vix spirali, pertinaciter affixa, 

 superjiciem matricis pariim erodente. 



Only one characteristic and one rubbed specimen were found 

 of tbis shell, Avbicb may be a Spiroglypbus. It bas however 

 some characters in common with the young of the great Cali- 

 fornian Vermetid, Aletes squamigerus. Long. '6, lat. apert. *13. 

 Hab. — Mazatlan ; extremely rare, on Uvanilla an^ Cuma ; 



L'pool Col. 



Tablet 1484 contains the characteristic sp. 



353. Aletes mabgasitaeum, Val. 



A. t. "A. centiquadro" simili, sed avfr. nucleosis iii. magis 

 elongatis ; anfr. normalihus rapide augentibus ; adulta sub- 

 quoidfatd, ad angulas carinis nodosis conspicue ornafd; liris 

 tenuioribus, vix decussatis. 

 Vermetus margaritarum, Val. Voy. Yen. pi. 11, f. 2. 



Only one adult and two extremely young sp. were found, 

 which may not be conspecific. The nuclear whirls are not 

 globular, as appears the case in the only specimen seen of V. 

 centiquadrus ; in this respect it is intermediate between that 

 species and Bivonia. Long. I'l lat. apert. '3. 

 Sab. — Mazatlan : extremely rare, on Spondylus ; L'pool Col. 



Tablet 1485 contains the youngest and the adult specimen. 



Gen PS VEEItlETUS, Adanson. 



Testa plus minusve spiralis. Operculum magnum ; extus 

 laminis concentricisfoliaceis instructum : intus marginem versus 

 canvexum ; cicatrice musculan circulari, concentrice calatd. 



Sen. p. 160, 1757.— IT. ^' A. Ad. Gen. vol. i. p. 357. 



Section A. Species typici. 



Testa janiore turritclloided. Operculo colore corneo, tenuiore, 

 extus foliaceo ; cicatrice concentrice Urulaia. 



The turritelloid Vermetida} form a small but natural group ; 

 of which the species are distinguished by the Bculpture of the 

 spiral portion, and of the operculum. 



