70 BULLETIN (50, UNITED STATES NATIONAL MUSEUM. 



There is no rostrum. 



The rostral latus is narrow, the scutal and Ixisal margins parallel. 

 Umbones at the upper front angle, aiid in contact. 



The inframedian latus is narrow, somewhat the shape of a wine 

 glass, a little expanded at the base and summit, narrower at the lower 

 third. Umbo median at the lower third. 



The carinal latus is of a curved triangular shape, the carinal margin 

 concave, baso-lateral margin convex. The apex projects well beyond 

 the carina, as in S. ^calpelhim^ etc. 



The peduncle is short, with about eight rows of live scales each. 



Length of the capitulum 29 mm., breadth 20 mm. Length of the 

 peduncle l-i mm. Length of carina 27 mm., diameter at base 5 mm. 



The mandible (Plate IV, iigs. 17, 18) has four teeth, counting the 

 lower point. The first tooth is rather widely separated from the sec- 

 ond. The lower point, shown more magnified in fig. 18, is obtuse, 

 ending in a group of fine spines. 



The first pair of cirri has unequal rami of 9 and 13 joints. The 

 shorter, anterior, ramus is about twice as wide as the other. Both 

 are densely hairy and spinose. 



The sixth pair of cirri has rami with about 36 segments. An inter- 

 mediate segment of the outer ramus is figured (Plate IV, fig. 15). There 

 is a series of long spines along the anterior margin, four on a segment. 

 These are paired with shorter spines on the inner face, shown in dotted 

 lines. There are also several short spines at the sutures. . The posterior 

 edge is very minutely spiculose, and has three spines on a segment, 

 the uppermost one large, the others quite small. There is also a row 

 of short spines on the inner face, more or less distinctl}^ visible through 

 the segment, and shown on the figure in dotted lines. The spines 

 diminish in size toward the bases of the rami, and in number toward 

 the apices, as in all other forms. 



The caudal appendage (Plate IV, fig. 16) consists of 6 joints, termi- 

 nating in a group of 6 long spines. There are also smaller spines at 

 the sutures. 



This species differs from others of the partially calcified group by 

 having only the terga V-shaped, and with the carina and lower whorl 

 of plates resembling species of the 8. scalpellinti group. S. compressmn 

 Hoek, from the equatorial Pacific, 2,150 fathoms, has some resem- 

 blance to imperfectum.^ and the antipodal 8. tntermedkmi also resem- 

 bles it except in the form of the carina and lower plates. 8. impei'- 

 fectum is very closely related to 8. aanctixharharx from the Californian 

 coast, but the carina of the latter has a less projecting umbo, its roof 

 is not so flat, and it is rounded at the base, and widely separated from 

 the carinal latera. The carinal latera do not project below the carina; 

 and, moreover, the plates of the lower whorl are more reduced in size 

 in 8. sanctdBharharse. 



