566 SUMMAKY OF CUKBENT RESEARCHES RELATING TO 



Tetraedron.* — Prof. A. Hansgirg revises bis monograph of this 

 genus of Algae, enumerating now twenty-seven species, arranged under 

 the four subgenera Polyedrium, Closteridium, Pseudostaurastrum, and 

 Thamniastrum, the first of these again consisting of two sections, 

 Eupolyedrium and Cerasterias. 



Movements of Diatoms and Oscillaria-j — According to the observa- 

 tions of Mr. W. A. Terry, the same species of diatom always occupies 

 the same position while in motion. Thus Stauroneis acuta always travels 

 with the valves vertical, showing the broad hoop or band and the edges 

 of the valves, as also do several species of Pinnularia and Surirella ; 

 while Stauroneis pTienicenteron travels with the valves horizontal, showing 

 one uppermost, as also do several species of Pinnularia, Surirella, and all 

 the species of Pleurosigma. The maximum rate of speed of diatoms is 

 stated to be a distance of about their own length in two seconds. 



The movements of Oscillaria cannot be explained, in the author's 

 opinion, by movements of the protoplasm, inasmuch as this is inclosed 

 in a rigid sheath. The proper motion appears to be an onward spiral 

 movement forward and backward in the direction of the length of the 

 filament, showing a striking resemblance to the motion of diatoms, and 

 probably produced in a similar manner. The waving and nodding 

 movements are always caused by the elasticity of the filament springing 

 back to regain its normal position while working itself free from 

 obstructions. 



Valve of Pleurosigma. J — Mr. T. F. Smith claims to have deter- 

 mined that the valve of Pleurosigma formosum consists of several layers 

 of structure ; the same is also true of P. decorum, halticum., and angu- 

 latum, and probably of other species of the genus. He recognizes three 

 types of valve-structure in Pleurosigma, viz. : — (1) a valve composed of 

 tvp^o layers of square grating, as P. halticum ; (2) a valve with two 

 layers of grating, with secondary markings placed diagonally, as P. 

 formosum ; and (3) a valve with two layers of net-like structure, as P. 

 angulatum ; and it is probable that all the species may be referred to one 

 or other of these types. 



Fossil Marine Diatoms.§ — Mr. C. H. Kain and Mr. E. A. Schultze 

 describe a remarkable fossil marine diatomaceous deposit from Atlantic 

 City, New Jersey, which includes also a few fresh-water forms. Several 

 new species are described, including possibly the type of a new genus. 



Synedra pulchella Ktz., var. abnormis.H — Under this name Sig. L. 

 Macchiati describes a remarkable form of this pleomorphic diatom, 

 agreeing with the type-form in the presence of a "definite annular 

 pseudo-nodule" or "median circle," but characterized by a singular 

 regular constriction near one end of the frond. The author proposes a 

 rearrangement of the species included in the genus, depending on the 

 fineness of the striation, and would separate the varieties macrocepliala 

 Grun. and naviculacea Grun. as distinct species. 



* Hedwigia, xxviii. (1889) pp. 17-9. Cf. this Journal, 1888, p. 1013. 



t Amer. Micr. Journ., x. (1889) pp. 81-3. 



X Journ. Quek. Micr. Club, iii. (1889) pp. 301-7 (1 pi.). 



§ Bull. Torrey Bot. Club, xvi. (1889) pp. 71-6 (1 pi.). 



II Nuov. Giorn. Bot. Ital., xxi. (1889) pp. 263-7 (2 figs). 



