Dear Doug,
Sinum minor (Dall, 1889) certainly is a valid species.
Apart from Abbott's Seashells of North America the species it is figured in
the Naticidae I card pack of Sally Kaicher:
Sally Diana Kaicher (1975) Naticidae I, Card No. 792.
 
The Smithsonian has the Type, USNM 86835, from  off Sombrero Key, Cape Florida,
84 fathoms, taken by R/V "Albatross" at stn. 2648, on mud, 7.3 x 5.6 mm.
There is also one Paratype USNM 87209, from Yucatan Bank, Gulf of Mexico.
An additional Paratype is at Harvard, MCZ 7509, from off Sombrero Island, at
54 fathoms, taken by R/V "Blake", 1878, 5.2 x 7.1 mm
 
In my colletion I have five specimens ranging from 7 to 11 mm which were all
dredged off Holetown on the west coast of Barbados, at 500-650 feet.
 
Hope this helps somewhat.
Best regards,
Michael
 
 
 
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