ART. 22 MIOCENE GASTROPODS AND SCAPHOPODS MANSFIELD 29 



ing, moderately inflated, constricted at the suture by a spiral 

 thread, and axially sculptured ^Yith about twelve narrow, pro- 

 tractive, intrasutural ribs. Postnuclear whorls w'ith a shallow, 

 grooved suture and sculptured mainly with the semikeeled. spiral 

 raised cords; a low keel is adjacent to and in front of the suture, 

 followed by two stronger, wide-spaced raised cords ; the anterior one 

 is stronger and constitutes the periphery of the whorl, and is situ- 

 ated on the lower half of the whorl, in front of which is a wide 

 rounded valley, bordered in front by a small postsutural keel. Axial 

 sculpture consists of many threadlike, mainly protractive, growth 

 lines, intercalating the spirals and extending up their slopes. On 

 the body whorl, there are in all about seven spirals extending from 

 the suture forward to the siphonal f asciole. Aperture rather wide ; 

 anal sinus apparently quite wide and shallow ; margin of outer lip 

 broken away, lirate wdthin; inner lip consisting of callus, the lower 

 margin is erect and forms the border of the short, reflected and 

 dextrally twisted siphonal canal. Siphonal fasciole prominent, 

 overrun by four spirals ; a small chink is behind the siphonal fasciole. 



Dimensions: Type (U. S. Nat. Mus. Cat. No. 352624) measures: 

 Altitude 6 mm, ; greatest diameter 2 mm. ; length of aperture 2 mm. 



An un described form in the United States National Museum col- 

 lection from Monkey Hill, Panama, is very similar to the new 

 species here described. It also belongs to the group of Microdrillla 

 hehetika Gardner (Ms.) from the Chipola marl member of the Alum 

 Bluff formation. 



Occurrence. — Middle or lower Miocene: In flood-wash, 1 mile south 

 of Brasso, Trinidad, British West Indies. 



MICRODRILLIA PROPETRINA, new species 



Plate 4, fig. 7 



Shell small, solid, rather stout consisting of two and one-half 

 nuclear and three postnuclear Avliorls. The first one and one-half 

 nuclear whorls broadly conical, porcellaneous, smooth, except for a 

 minute subsutural tliread; anterior nuclear whorl with a subsutural 

 band and marked with sharp arcuate riblets. Postnuclear whorls 

 w^eakly constricted at the suture and slightly inflated betAveen them ; 

 sculptured with three semikeeled, raised, spiral cords intercalated by 

 rather wide rounded valleys, the posterior one marginates the suture, 

 the medial and stronger one forms the periphery of the whorl, and 

 the third stands midway between the second and the suture, Axially 

 sculptured with fine, threadlike, arcuate, growth lines between tlie 

 spirals and extending up their slope. On the back of the body wliorl 

 there are seven spirals extending from the anal fasciole forward to 

 the siphonal fasciole. Aperture apparently wide; margin of outer 



