20 



BULLETIN 60, UNITED STATES NATIONAL MUSEUM. 



The upper lateral plate is subrhombic, the scutal and tergal mar- 

 gins straight and alwnt equal, the basal margin decidedly shorter, the 

 baso-carinal extremity rounded. The umbo is not quite terminal. 

 The rostrum is small ])ut well developed, in shape an isosceles trian- 

 gle. The rostral latus is transversely elongate, about twice as long as 

 wide, a little narrower ventrally, and divided by a low rib from the 

 apex to the baso-lateral angle. The inframedian latus is pentagonal, 

 a little longer than wide, with the umbo at the upper rostral third. 



The carinal latus is irregularly triangular, higher than wide, with 

 the umbo at the lower fourth, at the l)aso-lateral angle of the carina. 

 The peduncle has about li) rows of about 13 scales each. It is hir- 

 sute like the capitulum, and varies a good deal in length. 



Length of the capitulum 12.5, breadth 

 7 nun. Length of the peduncle 10 mm. 

 Length of the carina 10, diameter at 

 base 1.6 mm. (Fig. 5.) 



The figure and description are from 

 one of a group of six individuals from 

 Station 2906, most of them Avith the pe- 

 duncle much shorter — 6 or 7 mm. long. 

 When I described this form as a sub- 

 species of S. calif ornicvrit I had onl}'' 

 some young individuals less than half 

 the size of those now before me. The 

 larger examples show tiiat with increased 

 size the valves remain strongly calcified 

 to their borders, diti'ering from S. call- 

 forn'tcinn of equal size, in which the 

 valves are but weakly calcified, their 

 edges chitinous. These constant ditfer- 

 euces in the considerable series of both 

 Fig. o.-scALPELLUMossEUM. a, LATERAL foniis uow bcforc uic seem to indicate 



VIEW X 3; 6, DETAIL OF EOSTEUM. i rv . T . . • i i 



that aS. oHseum is a distmctspecies, though . 

 closely related to S. calif orn icv/m . A f ul 1 description of the adult form 

 of S. osseimi is given above to supplement my former account of the 

 young stage. 



The two species, californlcum and osseum, are related to the group 

 of S. scalpelJum rather than to that of S. stroemil., having the charac- 

 teristic low rostral latera and shoi-t rostrum of the former grou}). 



(IROtn' OF SOALI'l^XLUlNI STKOP^RIII. 



S. stroemli is the stmior name of a series of small Tsorth Atlantic 

 and Arctic forms, disting'uished . by the large pentagonal inframedian 

 latus with the umbo at or below the middle of its rosti-al bor- 

 der, a long and narrow or triangular but well-developed rostrum, 

 the rostral latus about as high as wide, subtriangular or quadrangu- 



\^ 



