The number of medial bristles on the caudal process were found to 

 vary considerably among specimens from the same locality and, 

 indeed, on opposite valves of the same specimen. In general, the 

 Atlantic and Pacific specimens are similar, each having a long poste- 

 rior and several smaller anterior bristles. 



First antenna (figs. 5e,f): 1st joint bare; 2nd joint with 1 spinous 

 dorsal bristle and 2 groups of short spines along dorsal margin; 3rd 

 joint with 1 dorsal bristle and without suture separating it from 4th 

 joint; 4th joint with 1 spinous dorsal bristle, 1 short and 2 long 

 ventral bristles, and 2 groups of short spines along ventral margin; 

 5th joint with stout sensory bristle; 6th joint with short spinous, 

 medial bristle; 7th joint with medium a- and b-bristles and long c- 

 bristle; 8th joint with d-, e-, f-, and g-bristles about same length as 

 sensory bristle on 5th joint. 



The 1st antenna of S. zostericola is described by Cushman (1906, 

 pi. 28: fig. 16) as having only 1 long and 1 short ventral bristle on the 

 4th joint because Cushman described a juvenile specimen. Cush- 

 man's description of the 1st antenna of S. americana (1906, p. 363, 

 pi. 27: fig. 3) shows it to be similar to adult specimens of S. zostericola. 



