486 Systematic Paleontology 



Family TURRITELLIDAE 



Genus TURRITELLA Lamarck 

 [Prodrome, 1799, p. 74] 



Type. — Turbo terebra Linne. 



A slender, polygyrate form spirally sculptured ; aperture holostomous, 

 oval or subquadrangular ; outer lip thin, simple, slightly produced ante- 

 riorly; columella simple, concave; posterior portion of shell vacant and 

 partitioned at each half turn. 



Turritella originated quite early in the Mesozoic and before the end of 

 the Cretaceous had become one of the more conspicuous elements in the 

 gastropod faunas of North America. The culmination of the genus 

 occurred, however, during the Tertiary, when it was represented by a large 

 number of very prolific species. The representation in the recent seas is 

 relatively meager, and confined, for the most part, to the warmer waters 

 of the Old World. 



A. Primary spirals more than three in number. 



1. Altitude of adult shell not exceeding 30 mm.; primary spirals fine 



and crowded; the secondaries microscopically fine. 



a. Later whorls convex; primaries usually five or six in num- 



ber Turritella bonaspes 



b. Whorls flattened; primaries twelve to fifteen in number. 



Turritella delmar 



2. Altitude of adult shell exceeding 30 mm. 



a. Primary spirals low, flattened, usually five in number, sepa- 



rated by interspirals of equal or greater width; whorls 

 convex, in the casts loosely coiled with well-rounded su- 

 tural channels Turritella paravertebroides 



b. Spirals approximately ten in number, subequal in size and 



spacing; whorls closely coiled, acutely angulated at the 

 sutures -. Turritella encrinoides 



B. Primary spirals three in number, very prominently elevated. 



1. Primaries sharp, laminar, very prominently elevated ridges, equal 



in size and symmetrically spaced; secondaries microscopic- 

 ally fine Turritella trilira 



2. Primaries cordate. 



a. Primaries asymmetrically spaced with respect to the sutures; 



secondaries fine but not microscopic Turritella tippana 



b. Primaries symmetrically spaced with respect to the sutures; 



secondaries only a little finer than the primaries. 



Turritella encrinoides 



Etymology: Diminutive of turns, tower. 



