392 Intelligence and Miscellaneous Articles. 



ther more than one half of the head, the latter being important for 

 the preservation of the vomer, so as to show the absence or presence 

 of teeth on that bone, and their form. All the essential characters 

 of the fish are consequently preserved, if care be taken that the skin 

 be so attached to the board on which it is dried, as to retain its ori- 

 ginal dimensions of length and depth : the due thickness of the fish 

 may be secured in the preparation, if it be considered desirable, by 

 inserting beneath the skin, when extending it on the board, a suffi- 

 cient quantity of prepared horse-hair. 



After explaining the mode which he had adopted in the prepara- 

 tion of the specimens exhibited, Mr. Yarrell made various remarks 

 on those which he regarded as the most interesting among them ; 

 and particularly on a series of Trout and Charr from diff"erent loca- 

 lities, and varying in colour according to situation, to season, and 

 also, in some instances, to food. 



He then directed the attention of the Meeting to the specimens of 

 the British species of Rays which formed part of the collection, and 

 pointed out particularly the difference, as regards surface, which ob- 

 tains in the sexes of many of these fishes ; the skin of the female 

 being, in every instance, comparatively smooth. He added also, by 

 reference to these specimens, and to specimens of the jaws exhibited 

 for that purpose, an explanation of the diff'erences which exist, in 

 adult indi\'iduals, in the teeth of the sexes respectively ; those of the 

 male becoming exceedingly lengthened and pointed, while in the fe- 

 male they retain very nearly their original flattened surface : the form 

 of the teeth, equally with the armature of the surface, constituting 

 in these fishes a secondary sexual character, although both the one 

 and the other have repeatedly, but erroneously, been considered as 

 adapted for the establishing of specific distinctions. 



LXV. Intelligence a?id Miscellaneous Articles. 

 ehrenbehg's fossil infusoria. 



MDUJARDIN laid before the Philomathic Society of Paris, 

 • some of the trlpoli or poller schiefer of Bilin in Bohemia, to- 

 gether with a microscope, by means of which it could be perceived that 

 this tripolj is formed, as M. Brongniart has announced from the infor- 

 mation of M. Ehrenberg, entirely of the siliceous remains of organized 

 bodies. 



These bodies, all proceeding from the same living species, appear 

 under two different forms : according as they are situated, trans- 

 versely or perpendicularly, they are minute rings, or rectangles en 

 echelle, with transverse bars corresponding to each ring : some of 

 those bodies, viewed obliquely, show well the identity of some with 

 others ; they originally formed articulated tubes, perfectly cylindrical, 

 from 1 to 16 thousandths of a millimetre in size, formed of contiguous 

 rings, whose height is less by half, and which each have an extremely 

 thin partition, as some broken rings show perfectly well; but, at the 

 present time, we find an analogous structure only in the Diatomae 

 which are placed by many naturalists in the vegetable kingdom, but 



