New Genera and Sjpecies of Diatomacese. By M. P. Petit. 239 
umbilicus occupying one-third of the entire diameter ; the valves 
appear striated under a low power, hut when more highly magni- 
fied the puncta are seen to have a quincuncial arrangement ; a ring 
of crossed striae surrounds the margin ; zone narrow and curved. 
Diameter 70 yu, 4 to 130 ya, umbilicus about 25 yu, to 50 yct. 
Campbell Island. PI. XIV., Fig. 7. 
This species is very variable in size ; the umbilicus is dark in 
colour ; with a low magnification the striae appear radiant, but under 
high - power objectives the puncta are found to be arranged in 
quincunxes. This arrangement, and the absence of dark robust 
striae starting from the umbilicus, distinguish this species from 
H. radiatus [Pyxldlcula radiata, O’Meara* * * § ). 
[M. Petit is correct in placing Podosira hormoides and P. macu- 
lata in the genus Hyalodiscus. Herr Cleve and M. Petit are, 
however, incorrect in making a distinct species of H. maculatus 
(P. maculata, Wm. Smith) ; it is identical with H. stelliger, Bailey, 
of which I have seen authentic examples (and perhaps with Cras- 
pedodiscus Stella, Ehr.). Professor H. L. Smith also confirms 
this.t 
It appears very doubtful to me whether H. suhtilis of Bailey is 
the same as H. Franldinii : his figure t represents a form with a 
small umbilicus and two sets of curvilinear striae intersecting each 
other like the engine-turning on the back of a watch. 
H. Franldinii (probably the same as H. californicus) has very 
fine radiating striae, certainly invisible with the objectives used by 
Bailey twenty years ago. 
H. subtilis is a much smaller form than the preceding : my 
specimens (from the English Channel and the Sandwich Islands) 
do not exceed in size the smallest valves of H. Franldinii, and the 
diameter of the umbilicus is not more than one-half the diameter 
of that in H. Franldinii. 
Discoplea umhilicata, Ehr., is perhaps the same as H. hor- 
moides. M. Petit refers Goseinodiscus punctulatus, Grreg., to 
H. stelliger. With this I do not concur ; Gregory would, I imagine, 
have been well acquainted with Podosira maculata of the ‘ Synopsis’ ; 
moreover, his figures and description § do not agree with H. 
stelliger. 
In one of the ‘ Tuscarora ’ soundings I have occasionally seen a 
disk only differing from Actinocyclus interpunctatus (Brightwell) in 
having a very small umbilicus. It also occurs in a gathering from 
the island of St. Paul, a slide of which was kindly sent me by 
M. Petit. 
* ‘ Jour, of Linn. Soc.,’ vol. xv., “ Diatom. Kerguel.,” p. 56, pi. i. fig. 9. 
t ‘ American Journal of Microscopy,’ vol. ii. p. 149. 
j ‘ Smithsonian Contributions,’ vii. p. 10, f. 12, 1853, 
§ ‘ T. M. S.,’ vol. V. pi. i. fig. 48 ; ‘ Clyde Diatoms,’ p. 28, pi. ii. fig. 46. 
