690 Transactions of the Society. 



•274 mm. (umbilicus "035 mm.), occurs rarely in the Sea of 

 Kamtscliatka. From St. Paul, Southern Ocean, PI. XXL, Fig, 4 a 

 (^Y^), Fig. 4 &, c (^^r^), structure of inner part and margin of 

 valve. 



P. stellulifera Grun., ' Casp. See Algen,' p. 35. — This form is dis- 

 tinguished from P. hormoides and P, maxima by a circle of larger 

 puncta (spines ?) near the margin of the highly convex valve which 

 has a broad border. The stellate appearance of the blank dots 

 is not always so obvious as in the specimen here represented, and 

 I have seen a specimen where the inner part very much resembled 

 P. hormoides. PI. XXI., Fig. 3 (^), Monterey deposit. 



[In the *Casp. See Algen,' p. 35, is the following additional 

 description. Diameter of valve, • OS mm. With the exception of 

 the irregularly punctate centre (about "01 mm. in diameter), 

 the valve has delicate radiating puncta (17-18 in "01 mm.). 

 The larger puncta are irregularly scattered, and have a peculiar 

 stellate appearance. The cell membrane is somewhat thick. The 

 large marginal puncta (spines ?), 4 in • 01 mm. This form, which 

 occurs in Herr Weissflog's collection, I name P. stellulifera.] 



P. Argus Grun., ' Casp. See Algen,' p. 35. — Valve highly 

 convex; diameter, '107 mm.; cell membrane very thick. The 

 inner concave valve is delicately striate; striae radiant (16 in 

 •01 mm). On the convex side is a sharply defined circular space, 

 with a finely dentate margin, within which are three to four 

 concentric circles of large oval dots (depressions?). California, 

 in the collection of Herr Weissflog. PI. XXL, Fig. 6 a (^ ■]''); 

 6 h, c, structure of inner portions and of the broad border of the 

 valve. 



Hyalodiscus scoticus (Kg.) Grun., in Cleve and Grunow's 

 'Arctic Diatoms.' {Cyclotella scotica Kg. ad specm. authent. 

 Podosira hormoides Wm. Sm. nee Mont. P. Franldini Grun., 

 ' Casp. See Algen,' p. 34.) I have, through the kindness of 

 Dr. Van Heurk, seen authentic specimens of C. scotica Kg. from 

 two Scotch localities. I am unable to say whether the G. scotica 

 from Constantinople, to which I alluded in the ' Casp. See Algen,' 

 p. 30, is identical, my preparation being mounted dry and 

 insufficiently cleansed, but the Scotch specimens are without doubt 

 the P. hormoides of W. Smith. I have never seen the granules 

 in the endochrome of this very common species, and there can 

 scarcely be any doubt of its belonging to the genus Hyalodiscus. 

 A stronger reason for uniting it to this genus is the absolute 

 impossibility of specifically distinguishing it from H. subtilis. 

 Anyone who doubts this has only to carefully examine the 

 Californian gatherings, or No. 2 of Cleve and Moller's from Finn- 

 mark, in which every possible intermediate form may be seen, to 



