192 "UNITED STATES NATIONAL MUSEUM BULLETIN 251 



Figure 83. — Siyela atlanlica (Van Name): a, the 18 mm. oval individual; i, the 15 mm. 

 individual with unusual peduncular prolongation; c, right half of mantle body of same 

 specimen, inner side; d, ciliated groove of a 13 mm., somewhat flattened, specimen; 

 e, entire appearance of same specimen; /, left half of mantle body of same specimen, 

 inner side. 



small proininencas, being apart from each other by about one-third 

 of body length. Test very thin, encrusted and impregnated with mud. 

 Inner surface whitish and glistening . Mantle thin, yellowish brown. 

 Atrial tentacles present. 



A 13 mm. long individual was dissected to make identification of 

 these flattened specimens certain. Inner longitudinal vessels of the 

 branchial sac are arranged (D= dorsal, V= ventral) : 



Left I) 2 (11) 5 (14) 4 (17) 5 (11) 2 V 



Right D 4 (22) 4 (12) 4 (IG) 5 (9) 2 V 



