498 Mr. W. H. Benson on some forms of Stenothyra. 



like which also it presents a faint oblique striation. These 

 shells are important as showing the occunence of the genus at 

 a distance of 300 miles from the sea, and 200 miles above the 

 extreme influence of the tides. 



4. Stenothyra frustillum, nobis, n. s. 



Testa vix rimata, minima, ovato-conoidea, politissima, sub lente obso- 

 letissime oblique striatula, albida, translucente, spira convexo- 

 couoidea, apice obtusulo, sutura leviter impressa ; anfractibus 4 

 convexiusculis, ultimo ventricosiore, minime compresso, dimidium 

 testae uon sequante, antice descendente, basi rotundata ; apertura 

 subrotundata, marginibus peristomatis acutiusculis. Operc. ? 



Long. \\, diam. 1 mill. 



Hab. in Australia. Mus. Cuming. 



5. Stenothyra strigilata, nobis, n. s. 



Testa non rimata, oblongo-ovata, solidiuscula, nitidula, oblique obso- 

 lete striatula, crebenime spiraliter sulcata, lineis brevissimis ob- 

 liquis excavatis (puuctorum loco) sulcos occupantibus, fu&co-nigres- 

 ceute ; spira ovato-conica, apice eroso, sutura impressa ; anfractibus 

 4 superstitibus convexiusculis, ultimo dimidium testae sequante, 

 antice valde descendente basi rotundata ; apertura ovata, subver- 

 ticali, intus livide cserulescente, peritremate obtuso, margine pa- 

 rietali intus callo, superne subito desinente, munito, dextro intus 

 longitudinaliter sulco marginato. Operculo tenui translucente, 

 concaviusculo, corneo, intus costa albida marginato. 



Long. 7, diam. 4 mill. 



Hah. in Insula Borneo. Mus. Cuming. 



This is the largest known species of the genus, and is a fine 

 addition to it. The cross linear sculpture of the furrows is dif- 

 ferent in character from that of the several species which present 

 puncticulate or foveolate lines. 



The operculum of Stenothyra has a calcareous skeleton or 

 basis, covered internally and externally by a horny layer, which 

 led to its designation by myself in 1836, and A. Adams in 1851, 

 as horny. According to Philippi, Gray states it to be calcareous, 

 and, on fracture, it will be found to be brittle, and that in some 

 species it does not yield to the knife like a horny substance, the 

 calcareous matter being predominant ; while in other very thin 

 and pellucid opercula the horny part is in excess. On the whole, 

 this part may be considered rather as of a mixed character than 

 as either strictly calcareous or horny. The structure of the 

 operculum is subspiral, and more analogous to that of Assiminia 

 and Hydrobia than to that of Bithinia. 



More extended characters of a few of the described species will 



