A FOSSIL MARINE D J ATOMACEOUS DEPOSIT. ' 67 



Porodiscus interruptus, n. sp., Gr. and St. — Valve circular, 

 very convex, with, clear central space about one -third of the 

 diameter of the disc. The rest of the surface covered with 

 radiating lines of distinct granules, interrupted near the margin 

 by a clear annular space, between which and the rim is a narrow 

 belt of closely-set granules. Margin clear. Diam. to '005". 

 Rare. PI. V., Fig. 8 (a small example.) 



BrigMwellia pulchra, Grun. (" Van Heurck Syn.," PI. 128, 

 Fig. 9). — Abundant, and very variable in size. Specimens 

 observed from -0025" to -0075" in diam. 



Podosira hormoides (Mont.), Grun. ("Kasp. Meere Diat.," p. 

 33). — A large coarse form which, but for the absence of the 

 large puncta, might be classed as P. stellulifera, Grun. Diam. 

 to '005". Not unfrequent. 



P. maxima, Kiitz. (Hyalodiscus, Grun., " K. M. Diat.," p. 33). 

 — Similar in general aspect to the type-form, but without the 

 usual traces of an opaque umbilicus. Diam. about '007". Not 

 rare. 



This form comes very near to Coscinodiscus. 



Hyalodiscus subtilis, Bail. (" Prit.," p. 815, PI. 5, Fig. 60).— 

 Varies greatly in size and in the proportionate diameter of the 

 umbilicus. Forms occur from "002" in diam. with a large 

 umbilicus resembling H. scoticus (Kiitz.), Grun., to '015" in 

 diam., with an umbilicus of "0084". The whole surface is 

 covered with lines of granules about 35 in "001". These large, 

 coarsely marked forms may be classed as var. robust a. 



H. radiatus (O'Meara), Grun. (CI. and Gr., "Arc. Diat.," 

 p. 117, also " F. J. L.," p. 41). — Smaller, and not so coarsely 

 marked as typical forms from Kerguelens Land. Not rare. 



H. arcticus, Grun. (" F. J. L.," p. 41, PI. E., Fig. 37).— 

 Frequent. 



Coscinodiscus radiatus, Ehr. (Grun., " F. J. L.," p. 19, and 20, 

 PI. C, Fig. 1, et seq.) — Frequent, with much variation. The 

 typical form is present, as well as vars. "major and minor, but 

 the most numerous variety is C. argus (I.e., p. 20, and " Atl.," 

 PL 61, Fig. 2), which passes into C. heteroporus ("Atl.," PI. 61, 

 Fig. 4) on one hand, and back to C. radiatus on the other. 



C. marginatus, Ehr. (Grun., I.e., also " Atl.," PI. 65, Fig. 3). 

 —From -003' to -0045" in diam., with thick-walled cellules 

 about 6 in -001". 



