

may, wo:.] OKAMURA.—CHAETO. & PERAGAL. OB' JAPAN. 93 



foramen, length of hoop, as well as by the direction and length 

 of horn-roots. In Ch.denticula.tum form of cell is cylindrical 

 with almost circular valve and the length is twice as long as 

 or more than the breadth, while in the present species cell is 

 rectangular in broader girdle surface having oblong valve and 

 the length is much shorter than breadth. Again, in the former, 

 foramen is small and vertically rhombic while in the latter it 

 is larger and transversely elliptic-lanceolate. 



Root of horn is longer in Ch. denticulatum and directed 

 almost vertically, while it is much shorter in C. nanodenticulatum 

 and decidedly diagonal. Again, in the former, hoop is a little 

 constricted and is very long and exceeds the half-length of the 

 mantle, while in the latter it is not constricted and is either 

 narrower than or equal as broad as the half-length of the 

 mantle. 



Thus, the differences between the two related species are so 

 numerous that one may not take the present species as a mere 

 broader form of Ch. denticulatum as Schroder thinks. We can 

 not also consider that these two forms are due to seasonal 

 variations, as it is case in Ch. decipiens Cleve, for they occur 

 in the same sample collected both at the same time and locality. 



The specimen shown in the annexed figure measures as 

 follows: length and breadth of cell, 22.5 ft and 45 ft respectively; 

 height of the mantle 15 ft and that of hoop 7.5 ft ; thickness of 

 spine 3.75 ft. 



Subgen. II. Hyalochaete Gran. 

 Section 3. Dicladia (Ehr.). 



10. C. Lorenzianum Grun. PL IV, Figs. 38-39. 



Cleve Treatise, 1897 a, p. 21, PL I, f. 13, 14, 15 ; Gran., 

 Diat., 1905, p. 76, f. 90.— C cellulosum Lauder, Hongkong, 

 1864, p. 78, t. 8, f. 12. 



Loc. in Jap. : Shirahama in Prov. Boshyu. 



Breadth and length in our specimens measure 27-35 ft and 

 20—35 ft respectively. The specimen shown in Fig. 38 a measures 



