1855.] Chusan Shells. 133 



" From the coast of Chusan. Some were brought to Dr. Cantor 

 from the entrance of the canal ; but he did not himself find them 

 in the estuary." 



This shell does not agree with the characters of any of the sub- 

 genera of Cerithium in which Lamark and Gray have placed it, 

 and the structure of the base of the columella is almost precisely 

 that of Planaxis, Lamarck, from which the form is sufficiently dis- 

 tinguished by the truncation of the base of the aperture, its sinuous 

 outline, and the absence of the interior ribs, as well as by the 

 elongated form of the spire. Swainson has considered Planaocis to 

 be a terminal genus of the Melaniance, and the present species in 

 its form and sinuous lip presents characters in consonance with the 

 typical species of Melania, while the columella approaches to the 

 structure of that of Melanopsis. As in Planaxis and many of the 

 Cerithina, there is a callus attached to the penultimate whorl near 

 the top of the aperture, and its scabrous surface and occasional 

 disposition to form a varix on the last whorl behind the pillar, give 

 a farther resemblance to that sub-family. 



Laguncula, Nov. Gen. 



Testa turbinata, subglobosa, apertura majori, integra, oblonga, 

 peristomate interrupto, labio subreflexo ; umbilico profundo, tortuoso. 



Laguncula pulchella, Benson. 



Testa albido-glauca, ovato-globosa ; anfractibus convexis, lineis 

 longitudinalibus, elevatiusculis, aliis obliquis decussatis, instructis ; 

 suturis impressis ; apertura intus fascia lata pallide-castanea ornata, 

 columellaque intus concolori. 



" Asserted to be an inhabitant of the canals at Chusan, and 

 found under the same circumstances as Venus chinensis." 



The raised lines crossing each other, give the facet-like appearance 

 to the surface, which is frequently observable in Limnaea. The 

 form of the umbilicus and the greater prominence of the raised 

 lines near the umbilicus shew an approach to the subgenus Globu- 

 laria. Whorls 5, exclusive of the apex, which is less acute than in 

 Assiminia. The substance of the shell is thin, and it lias much 

 the aspect of a shortened Paludina, such as P. crassa. It appears 



