J 00 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Body oblong or oval, more or less compressed laterally, attached by 

 an area at or near the posterior end. Apertures both 4-lobed, quite 

 widely separated, the branchial larger and nearly terminal, the atrial 

 well back on the dorsal side, both but slightly if at all prominent in 

 the preserved specimens. Test rather thin, dirty whitish in color; 

 in the specimens preserved in formalin rather soft and flexible, but 

 with a tough external layer. Surface wrinkled, bearing considerable 

 adherent sand and mud ; inner surface slightly pearly. Largest speci- 

 men 25 mm. long, 20 mm. in dorso-ventral diameter, and 12 mm. (esti- 

 mated) from side to side. 



Mantle musculature only moderately developed, very diffuse, con- 

 sisting of separate fibers which cross each other in various directions, 

 forming on most parts of the body a fairly continuous layer without 

 being gathered into conspicuous bands. Even the muscle fibers radi- 

 ating from the base of the tubes remain separate, or form only very 

 small groups. They are overlaid by circular fibers. 



! 51 



Figs. 50-52. — Pandocia qdadrata (Herdman). 50, Left and right sides of body. Nat- 

 ural size. 51, Dorsal tubercle. X 10. 52, Gonad. Side attached to mantle. 

 X 10. 



Tentacles of several sizes but arranged with little regularity. 

 Over 20 of them are fairly large; some small ones are also present. 



Dorsal tubercle small, its orifice elongated, forming a slightly S- 

 shaped curve. 



Dorsal lamina fairly wide ; plain edged. 



Branchial sac with four well-developed folds on each side, the 

 fourth lower than any of the others. Transverse vessels numerous, 

 somewhat variable in size, but in most parts of the sac little regu- 

 larity of arrangement other than an alternation of larger and smaller 

 ones is noticeable; the latter generalty only cross the stigmata in 

 some parts of their course; in other parts they become stouter and 

 divide them. Internal longitudinal vessels very delicate, narrow, 

 and inconspicuous. The following is an approximation to their 

 arrangement on the left side of one specimen : 



dorsal 7 (20) (13) 5 (16) 5 (10) 6 ventral. 



On the intervals between folds about 4 stigmata intervene between 

 the internal longitudinal vessels in the dorsal region, and about 6 

 in the ventral region. On the right side of the above specimen a 



