498 Miscellaneous. 



sulcato. Caput antice deflexum, fronte semicirculari marginato. 

 Mandibulce membranacece ? MaxillcB cornea, lobo apicali in un- 

 guiculum curvatum acutissimum producto. Antenna 9 -articulated. 

 Prothorax fere rotundatus, antice truncatus, medio profunde sul- 

 catus. Elytra apicibus setosis, singula 4-sulcato. Pedes lati, com- 

 pressi, tibiarum apicibus angulatis. 

 Chaetopisthes fulvus, Westw. Fulvus, nitidus, capite et prothorace 

 parum castaneis, hoc angulis posticis basique transverse impressOy 

 impressionibus setulosis. Long. corp. lin. 1|. — Hab. in India 

 Centrali. D. Boys. 



A memoir on the characters and geographical distribution of those 

 groups in nature which are considered as typical of families, by 

 G. R. Waterhouse, Esq., was also read, which led to an extended 

 discussion on the geography of insects. 



MISCELLANEOUS. 

 Apparatus of Hearing in Mollusks. By Dr. Frey. 



The observations of Dr. Frey have been especially directed to the 

 embryo of Limnceus stagnalis. The auricular vesicle is not percep- 

 tible in this mollusk until the singular rotatory movements of the 

 embryo have ceased, and when the animal already crawls on the in- 

 ternal side of its shell. It is easy then to observe, on the anterior 

 part of the body, the rudiments of the tentacles, the eyes with their 

 pigment, and the tongue with its characteristic epithelium. On 

 each side of the base of the tongue are found the auditory vesicles. 

 They are spherical, their contour is simple, and their diameter from 

 ^ to ^ of a line. At first they appear to contain in their interior only 

 a transparent liquid, and are then, like the eye, unconnected with 

 the central parts of the nervous system. There are soon developed 

 in the liquid one or two small corpuscles, the form, the size, and the 

 oscillatory movements of which are quite similar to those of the 

 otolithes of the perfect animal ; the vesicle which contains them pre- 

 sents on its margin a double contour, resulting probably from the 

 thickness which the sides acquire. The size of the otolithes is from 

 4To *^ Too °^ ^ 1^^^ 5 their number slowly increases, and reaches to 

 20 when the Limnceus quits its shell ; the diameter of the vesicle is, 

 at this period, J^- of a line. By the side of the otolithes occur other 

 smaller corpuscles, which often do not attain the size of yoVo °^ ^ 

 line. The number of the otolithes and the size of the auditory vesi- 

 cle continue afterwards to increase, at the same time that the ani- 

 mal increases ; in the adult state, from 100 to 200 otolithes may be 

 counted, and the diameter of the vesicle varies from -^^ to -^^ of a 

 line. 



The development of the auditory apparatus presents the same 

 phsenomena in Physa, Paludina and the terrestrial Gasteropods in 

 general (Helix, Limax, &c.) ; the only differences are in the size of 

 the parts. 



In the bivalves, the apparatus of hearing only contains a single 

 otolithe of large dimensions, which fills the cavity of the vesicle. 



