MARINE DIATOMS OP THE PHILIPPINE ISLANDS 133 



found it also at Puna, Hawaii, the Hawaiian specimens being relatively 

 narrower, as their ratio of length to width is sometimes as high as 

 17 to 1. 



Type— Cat. No. 43669 U.S.N. M. 



PLEUROSIGMA AFFINE Grunow 



(Van Heurck, Synopsis, pi. 18, fig. 9; Peragallo, Pleuro, pi. 4, figs. 2, 3, 5, 8.) 



Neither Ralf's P. normanii nor H. L. Smith's P. virginicum should 

 be included here, although so grouped by Peragallo. 



PLEUROSIGMA ANGULATUM W. Smith 



(Smith, Brit. Diat., pi. 21, fig. 205; Peragallo, Pleuro., pi. 5, figs. 3-5; H. L. 

 Smith, Types, Nos. 389-390.) 



De Toni (Syl. Alg., pp. 231-234) has attempted an impossible con- 

 densation of species under this head. Peragallo, with some reason, 

 expresses doubt of the general custom of considering P. quadratum 

 as a variety of P. angulatum. 



PLEUROSIGMA BALTICUM (Ehrenberg) W. Smith 



(Smith, Brit. Diat., pi. 22, fig. 207; H. L. Smith, Types, No. 396; Peragallo, 

 Pleuro., pi. 7, figs. 19-20.) 



PLEUROSIGMA DOLOSUM, new species 



Plate 29, fig. 6 



Valve narrow elliptical, not sigmoid, ends not produced, blunt, 

 rounded; markings quincunx; rhaphe straight, outer ends beaded, 

 reaching to the margin ; central area small, oval not laterally extended. 



Length 0.083; width 0.015; 25 lines in 0.01 mm. 



Jolo Jolo, Sulu Islands; rare. 



This very divergent species of the true Pleurosigmae differs from 

 others only in its Naviculoid form. Under low magnification it might 

 easily be overlooked as a rather minute specimen of Navicula iridis 

 Ehrenberg. But its rhaphe, central area, and delicate, uniform 

 quincunx marking fix clearly its generic character. 



Type.— Oat. No. 43670, U.S.N.M. 



PLEUROSIGMA ELEGANTISSIMUM Castracane 



(Castracane, Chall. Exp., p. 37, pi. 28, fig. 1; Peragallo, Pleuro., pi. 5, fig. 23.) 



A slightly doubtful specimen of this diatom was found; the origi- 

 nal was from Yeddo Bay, Japan. The uncertainty comes from Cas- 

 tracane saying that his species has extremely delicate striae, "striis 

 delicatissimis" ; but as no measurements of these are given the exact 

 meaning of the expression can not be determined. The peculiar shape 

 and the eccentric rhaphe indicate that the Philippine specimens and 

 the above are the same. 



