684 Trayisactions of the Society. 



margins ; tlie puncta (spines) submarginal ; the radiating striae on 

 the inner part of the margin 11 in -01 mm., on the outer part 

 about 13 in -01 mm. The centre is marked with (excepting a 

 small speck in tlie middle) deHcate radiating puncta. 



To G. Bodanica Eulenstein joins a not uncommon North 

 American Oyclotella, which is distinguished by its smaller size 

 and more distant punctate lines in the centre, and which I at one 

 time called var. affinis. 



C. Dallasiana W. Sm., a common form in brackish water 

 localities; it is distinguished from C. operculata by its much 

 greater size, stronger striation of the marginal band (9-12 in 

 •01 mm.), and a semicircular arch of larger puncta on the edge of 

 the irregularly punctate centre. [The puncta are distinct on the 

 specimens from Para River, but their presence is doubtful on those 

 from many other localities. — F, K.] To G. Dallasiana may possibly 

 belong Goscinodiscus striatus Kg. and Discoplea sinensis Ehr. 

 Dr. Arnott, in his note on the genus Cyclotella, ' Q. M. Journal,' 

 vol. viii. p. 247, refers G. stylorum * Brightwell, ' Q. M. J.,' vol. viii. 

 p. 9'), to G. Dallasiana. Brightwell's form I know well, and have 

 seen the original specimen from which the figure (a very indifferent 

 one) was made. The G. Dallasiana of Smith, of which I have 

 also seen authentic specimens, differs considerably from G. stylorum. 

 The marginal band is narrow and finely striate ; the large granulate 

 centre is undulate, but not the whole valve. G. stylorum also 

 shows this, but in a much less degree. In the latter the marginal 

 band is much broader, the stria3 stronger, and the valves much more 

 robust ; it is moreover a much commoner form. I have it from many 

 North American localities, the Para Ptiver mud, South America, 

 and in mud from the mouth of the Eokelle, Sierra Leone (where Mr. 

 Brightwell first observed it). I do not know of any British habitat. 

 C. Dallasiana, on the contrary, is much less common. • Smith 

 found a single specimen in a slide of a gathering from the Medway. 

 Mr. Roper detected it in Thames mud. It also occurs in the Para 

 River mud. I know of no other habitats. Those from the Para 

 are very fine, and the depression and elevation of the centre very 

 distinct. I am disposed to refer the form called by L. W. Bailey f 

 Gymatopleura (?) Campylodiscus, to this species. His description is 

 as follows : — " Large, lateral view almost circular, sometimes broadly 

 oval (his figure is perfectly circular ; the oval appearance might be 

 caused by the valve being tilted) ; marginal strife short, close, and 

 showing under a high power gland-like dots. Lateral valve with 

 one deep undulation, surface finely striated. Hab. Honeylake 

 VaUey, foot of Sierra Nevada." 



* In the work referred to, Dr. Arnott says C 7-adiata: this is an error; in the 

 wipics of his paper (privately distributed) lie alters it to stylorum, 

 t ' Boston Journ. of Nat. Hist.,' vol. vii. p. 350, pi. 8, fig. F. 



