vol. 2, pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 65 



strands of the atrial sphincters, which are so close together that they 

 seem to form a broad band continuous over both lips of the atrial 

 aperture. The fibers of this atrial sphincter are less closely approxi- 



Cl.6'.19 



••-■Vr 



■'■••■=•■:■ VIS 

 :: - ■■■■. w 



us. zi i 



FlG. 37.— iiiTTERIA HEXAGONA, SOLITARY FORM, ATRIAL MUSCLES, VIEWED FROM THE LEFT SIDE. X5 

 DIAMETERS. (DRAWN BY HOYT S. HOPKINS.) 



mated than are those composing one of the body muscles, the fibers 

 not actually touching side by side in the former while they do in 

 the latter. 



Fig. 38.— Ritteria hexagona, solitary form, the gut viewed from the right side, x 3J dlame 

 ters. (Drawn by Hoyt S. Hopkins.) 



Ventral to the base of the atrial retractor muscle are several 

 branching muscle strands not observed in other species. 



Tho gut (fig. 38), as in the other solitary Ritterias, is a simple loop. 

 In R. hexagona there is a bend where the esophagus enters the intes- 



