372 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 97 
2, Dissection of anterior portion of body, 4/5. The posterior boundary of 
introvert is at J; frenulum F has been omitted; +, on constricted posterior 
*“ region indicates end of intestinal spiral when in the body naturally. 
3, 4, Introvert spines: 3, Curved spine from posterior part of area, X 50; 4, 
nearly straight spine from first three rows, 0.32 mm. long, X 100. 
5, Diagram of tentacles showing the grooves, which are bordered by 5 to 7 
grooved pinnae (not indicated), X 2%. 
6, Longitudinal section of body wall from posteror region, X 5. The longi- 
tudinal muscle band below is not a section but a side view of the bundle. 
A, anus; C, intestinal coecum; CC, circular coelomic canal with arrows in the 
entrance from body coelom; CV, dorsal contractile vessel (there is no ven- 
tral); J, posterior boundary of introvert; F, F’, frenula; LC, longitudinal 
canals; N, nephridium; NC, nerve cord; NO, nuchal organ; O, the dorsal, 
and O’, the ventral side of esophagus; R, rectum, RV, retractor muscles; 
S, spindle muscle; W, small fan muscles of rectum. 
PuatTE 14 
Siphonomecus ingens, new species 
1, Head of a small specimen (Elkhorn Slough, Monterey Bay, Calif.) drawn 
from life, < 8. 
2, Anterior end of paratype, X 1, showing the introvert partly invaginated 
and retractors in contracted state. 
3, Portion of 2 enlarged X 2d. The left dorsal frenulum F’ has been severed. 
4, Nephrostome of a specimen from Newport Bay and associated coelomic 
papillae, < 10. 
5, Coelomic papilla, X 30. 
6, Brain of paratype, X 10. 
CP, coelomic papillae; CV, dorsal contractile vessel; F, frenula or fixing muscles; 
F’, left dorsal frenulum; F’’, right dorsal frenulum; J, introvert; N, neph- 
ridium; NC, nerve cord; NO, position of nuchal organ at anterior end of 
dorsal double series of tentacular lappets; O, esophagus; RD, dorsal retractors; 
RV, ventral retractors; S, spindle muscle; W, fan muscle of rectum. 
PuatE 15 
Siphonomecus ingens, new species: Type 
1, 2, Anterior half of body X 1.5. The top of fig. 2 is a continuation of the bottom 
of fig. 1. This specimen is unusually well relaxed. The coelomic papillae 
have been omitted and the muscle bands are only lightly indicated in order 
to avoid confusion of lines. 
3, Same specimens, X 3. Point where the esophagus joins and is fastened to 
the ascending intestine at end of rectum, showing relations to spindle muscle 
(S) and dorsal frenula F’ and F’’, the ventral frenulum to esophagus is 
omitted. 
4, Segment of the esophagus and four retractors opposite the fan muscles of 
rectum to show the lateral mesenteries of esophagus, X 5. M, right mes- 
entery. 
Other lettering as for plate 12. 
U.S. GOVERNMENT PRINTING OFFICE: 1947 
