OP CONCHOLOGY. 295 



A distinct species, easily recognized from its curved shape and 

 character of last whorl. 



MucRONALiA GRACILIS, Peasc. Plate 24, fig. 27. 



Description. — T. solida, polita, nitida, elongata, turrita, alba ; 

 anfr. 7, rotundato-convexis ; sutura bene impressa ; apertura 

 oblique ovata ; columella siibcallosa. 



Dimensions. — Long. 4, diam. 2 mill. 



Locality. — Tahiti. 



Shell solid, polished, shining, elongate, turrited, white ; whorls 

 7, convexly rounded, suture well impressed ; aperture obliquely 

 ovate ; columella slightly callous. 



The most slender of this genus. 



RissoiNA COSTULATA, Pease. Plate 24, fig. 28. 



Description. — T. elongata, fusiformi, gracilis, longitudinaliter 

 valde costata, transversim striata ; anfr. plano-convexis ; sutura 

 bene impressa, sulcata ; apertura parva, ovata ; alba, anfr. medio 

 fascia castaneo-fusca cingulatis. 



Dimensions. — Long. 5, diam. 2 mill. 



Locality. — Paumotus. 



Shell elongate fusiform, slender, longitudinally prominently 

 ribbed, striate transversely ; whorls flatly convex ; suture deeply 

 impressed, grooved ; aperture very small, ovate ; Avhite, encir- 

 cled by a chestnut brown band on middle of whorls. 



RissoiNA SEMIPLICATA, Pease. (Proc. Zool. Soc. London, 

 1862). Plate 24, fig. 29. 



Description. — T. subulata polita, nitida, subpellucida, alba ; 

 anfr. 6, plano-convexis ; spira longitudinaliter-plicata ; apertura 

 ovata, subeffusa ; columella vix callosa. 



Dimensions. — Long. 3|, diam. 1| mill. 



Locality. — Insl. Howland. 



Shell subulate, white, shining, polished, subpellucid ; whorls 

 6, flatly convex ; spire longitudinally plicate ; aperture ovate, 

 slightly efl"use ; columella slightly callous. 



RissoiNA TENUISTRIATA, Pease. Plate 24, fig. 30. 



Description. — T. solida, subulata, alba, longitudinaliter cre- 

 berrime tenuistriata ; anfr. 6 — 7, convexis, ad suturam vix de- 

 pressis marginatis ; anfr. ultimo magno, dimidiam longitudinis 



