9 



TRUNCATELLA 



A genus of unisexual, amphibious, snails, mostly tropical. 

 They occur near the sea, on sea-weeds thrown up on the 

 shore, among rocks, or in shallow water. Animal with eyes 

 at the rear of the base of the two contractile tentacles. Shell 

 small, cylindric or pupoid, with small oval aperature and 

 thin spiral operculum. Whorls transversely ribbed. As the 

 animal approaches maturity, the upper portion of shell 

 breaks off, the animal closing up behind it with a calcareous 

 deposit when it abandons the outgrown parts. On account 

 of this truncation of the shell, the genus has received its 

 name. About 100 species have been described. Named by 

 Risso. 



80 Truncatella californica 



Shell imperforate, thin, translucent, slightly striate; de- 

 ciduous part of about 5 whorls, acute, gradually enlarged to 

 a maximum of 2 mm; the mature shell usually of about 4 

 whorls, quite convex, the last one not carinate below; aper- 

 ture vertical suboval, lip simple, continuous, slightly ex- 

 panded ; mature shells of a maximum diameter of 2 mm, 

 and length of 5, the whorls nearly uniform. The young 

 shells attain a length of 5 mm before it begins to cast off 

 its outgrown whorls. 



Type locality: San Diego, California. 



In November, 1913, the writer turned over a discarded 

 coat on the edge of a flat subject to tidal overflow from the 

 waters of San Diego bay, and in a space of about a cubic 

 foot, in the folds of the coat, and in the honey-combed mass 

 of decaying sea-grass beneath, discovered a colony of fully 

 10,000 of these beautiful shining, amber-colored shells, the 

 white animals being quite lively, and in all stages of de- 

 velopment. 



Not rare at Santo Domingo, Baja Cal. 



81 Truncatella stimpsonii 



This I found in considerable numbers in company with Pedi- 

 pes unisulcatus, on and under smoothly-worn boulders in caves 

 on the ocean beach south of La Jolla, Cal., near high water mark. 

 Very common at Santa Domingo, Baja Cal. 



82 Pomaulax undosus 



Shell 4 inches or more in height and diameter; shell of whitish 

 pearl covered with a brown, fibrous epidermis; operculum horny 

 within, outside strengthened with two heavy, curved ribs; whorls 

 varied by numerous wavy ridges, and base ornamented with 

 beaded circles. 



Santa Barbara, Cal., to Cape San Lucas; common at San Diego 

 and at Santo Domingo, Baja Cal. Cedros Island. 



Quaternary: — Santa Barbara, Cal., to San Quintin, Baja Cal.; 

 Borrego Springs, Colorado Desert. 



