MODULIDAE AND TrIPHORIDAE 139 



angled at keel of body whorl; outer lip thin, crenulate; columella 

 with sharp horizontal basal tooth; operculum corneous. 



Modulus modulus floridanus Conrad PI. 27, figs. 188a, b 



Alt., 13; diam. of base, 14 mm. General characters of M. mod- 

 ulus; whorls more convex, peripheral keel less marked, about 15 

 radiating ribs; aperture round, oblique to vertical axis; columellar 

 tooth slightly oblique, a little smaller and lower than in M. modulus. 



Both M. in. floridanus and M. modulus are common on grassy 

 bottoms m shallow, protected waters. 



Family TKIPHORIDAE 



Some hundred species are included in this family of small mol- 

 lusks. Their distribution is general through warm and temperate 

 seas. With members of the related family Cerithiopsidae, they have 

 a considerable range in depth. 



The shells are sinistral, slender, with many whorled, elongate 

 spire and a somewhat contracted body whorl with small aperture 

 and short recurved canal. 



Genus TKIPHORA Desliayes, 1824 

 Triphora perversa nigTocincta-*^ (C. B. Adams) PI. 27, fig. 189 



Alt., 11 mm. Shell small, sinistral, cylindro-conic; apex acute; 

 dark brown; faded shells pale brown with dark revolving band; 

 from 12 to 15 whorls, not well defined; sutures slightly excavated; 

 sculpture of three sometimes four roundly beaded spirals; with a 

 lens, beads are seen to be light-colored, lower part of body whorl 

 with strong revolving ridges; aperture oval, oblique, deep posterior 

 notch; short, recurved anterior canal; outer lip thin, sharp, a little 

 flaring; operculum corneous. 



In fully adult shells both the anterior canal and posterior notch 

 become completely tubular, and growth of the body whorl continues 

 for about one-half turn beyond closing of canals. In juvenile shells 

 the base of the body whorl is flat, the aperture simple; all stages of 

 development of adult characters of aperture and canals may be seen 



-■'^ Gr., //-/, thrice; phora, from Gr. phoreln, to bear, denoting a group 

 wiiicii bears a special feature; Lat., pervrrsus, turned the wrong way; 

 nigcr, black; cinctiis, encircled. 



