1S8 Mr. C. Mercschkowskj on ScUaphora. 



regular spliere; usually tlicy arc more or less irre2;ular, 

 annular, souictiuies elongated. A very interesting peculiarity 

 ot these libroplasts is their constant motion. They are cou- 

 tnuiously wandering along the median line, now approaching 

 the extremities, now reaching the border of the central part 

 of the j)late. The two little crosses in fig. 4 mark the limits 

 ot their wanderings. These movements do not ])rocced in 

 a regular way, but are rather irregular, with sudden changes 

 in both directions. 



The same kind of libroplasts are to be found in many 

 diatoms ; they occur in several species of Naviciild and 

 Caloneis, are common amongst Di'ploneis and Amphora, and 

 are never absent in 2'ropidoneis, Pleiiros'igma, and To.conidea ; 

 usually also they have the same kind of movements. 



The central plasma is not well marked, being hidden by 

 the median part of the chromatophore ; it can be better seen 

 in the zonal aspect, where it appears as a narrow transverse 

 band (fig. 2, pi). 



In order to give an idea of the structure of the valve of at 

 least one species of this genus I have reproduced here the 

 figure of a valve of S. papula after Grunow* (tig. 5). 



As already stated, I have observed a great number of 

 living specimens of this species in fresh water in Los Angeles 

 ((California). 



Some measurements in millimetres are : — 



Length: 0;021 0-024 0-0276 0033 033 



Breadth of valve: O-00S6 OOOSG 0-0095 0()09o 0-009.3* 



Cleve t distinguishes the two foHowing varieties: — 



Var. rectangularis, Greg. (M. J, ii. pi. iv. fig. 17, IS >t ; 

 Grun. A ret. D. ]). 45). 



Var. bacillarioides, Grun. (Cl., Grun. Arct. D. 18S0, 

 p. 1.3). 



Sellaphora Borscowii, sp. n. (Pi. IV. figs. 6-10.) 



Valve narrow, linear-lanceolate or almost linear, slightly 

 attenuated at the ends, which are a little ])roduccd, broad and 

 roundly truncate. Terminal nodules distant from the ends. 

 Stria3 very fine. Frustule delicate, regularly quadrangular, 

 with truncate ends and rounded angles. Lives in gelatinous 

 tichizunema-Wkc, tubes. Length 0'019-0031 mm., breadth 

 ot valve 0-0052-0 OOG 7 mm. 



]\Iarine : iSan Pedro (Calil'ornia) . 



* Cleve & Grunow, Arctische Diat. pi. ii. lig. 03. 

 t Cleve, Syn. Navic. Diut. part i. p. 131. 



