Dec. 1, 1867.J 



HARDWICKE'S SCIENCE-GOSSIP. 



m 



resting question, whether the spider may not have 

 the power of ejecting or withholding the poison at 

 will, in which case your correspondent's opinion 

 that flies killed for food are not poisoned may be 

 correct. The examination of the orifice near the 

 end of the fang (or first joint of the mandible) is a 

 less easy matter, but it is a mistake to say that it 

 cannot be seen by transmitted light. If it were a 

 simple perforation, of course there would be no 

 difficulty, but beiug only an opening into the channel 

 of which it is the termination, it is necessarily rather 

 obscure. Still, I have traced it in a specimen 

 mounted in the ordinary way in balsam, and if 

 glycerine jelly be used, it can generally be seen 

 readily enough with an inch object-glass. 1 shall be 

 most happy, if your correspondent lives in London, 

 and will drop me a line, to show him both bag and 

 orifice. John T. Young. 



32, Mount Street, New Road, Whitechapel. 



angles much produced ; frequently mixed with the 

 typical form. 



Var. y, with five incurved sides, and only differs 

 from the preceding variety by the greater number 

 of sides. This variety appears to be rare, as I know 



THE GENUS AMPHITETRAS. 



fTlHE genus Amphitetras was constituted by 

 -*- Ehrenberg for the reception of those species 

 of Diatomacese whose frustules assume a cubical 

 form. This geueric distinction has, however, been 

 rendered valueless by the discovery of four-sided 

 varieties of Triceratium. Professor Smith says that 

 "the projection of the connecting membrane beyond 

 the suture of the valve is a circumstance that first 

 meets us in this genus." This characteristic is not, 

 however, peculiar to the genus Amphitetras, as it 

 occurs in Biddulphia. 



The mode of growth (in zigzag filaments) was at 

 one time considered of sufficient importance to re- 

 move it far apart from its near relation, Triceratium ; 

 but the discovery of a species of Triceratium grow- 

 ing in zigzag chains has destroyed that distinction. 

 A valued correspondent of mine states it as his 

 belief that all recent species of Triceratium will 

 ultimately be found growing in that manner ; but 

 whether the genus Amphitetras should be merged 

 in that of Triceratium, or the two genera formed 

 into a new genus with somewhat enlarged generic 

 character, is a question which will require a more 

 perfect knowledge of the two genera than we at 

 present possess. The species and varieties I am 

 about to describe I think belong to the genus Am- 

 phitetras as at present constituted. 



Amphitetras autediluviana. — The so-called typical 

 form of this species has cubical frustules, cohering 

 at the angles, forming a zigzag filament ; valve 

 square, with straight sides, and the angles more or 

 less rounded; the surface has coarsely cellular 

 markings. This species is variable in size and 

 widely distributed. 



Var. /3 has the sides deeply incurved and the 



Fig. 283. Amphitetras antediluviaua, var. y. *^ J^ £ & , 



of only one locality in which it has been found, viz., 

 Hayling Island, Hants, in which it was rare, a and 



(3 were more plentiful in it. (Fig. 283, x 400diam.) 

 Dr. Greville describes and figures, in the "Tran- 

 sactions of the Royal Micr. Soc.," vol. xiii., pi. ix., 

 fig. 27, a form which he calls Amphitetras nobilis, 

 and which seems to differ from var. y in the pro- 

 duced tubular apices. His species was detected iu 

 dredgings from the Red Sea. 





QS -i j:.:..;.i i :»..r 



Fig. 284. Amphitetras autedi- 

 luviana, var. S x 400. 



Fig. 285. Amphitetras 

 crucifera, x 800. 



Var. o, with three straight or slightly convex sides, 

 angles widely rounded ; in other respects like the 

 typical form. Rare; in a small gathering from 

 Joppa. (Pig. 284, x 400 diam.) 



Amphitetras crucifera. — Valve minute, with pro- 

 duced mammiform apices ; surface of valve minutely 

 punctate, with a cruciform blank space extending 

 from the centre to the angles. Cleanings from West 

 Indian shells. (Fig. 285, x 800 diam.) 



Amphitetras ornata (?) var. (i. — Valve with sides 

 slightly incurved; angles produced, mammiform. 

 Central portion of valve reticulate and punctate ; 

 the broad portions of the angles apparently girt 

 with a punctate and costate band. This variety 



