498 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
square aperture, surrounded by a circle of dull reddish brown. In 
contraction the tubes are not retracted but are usually shortened to 
about one-half their length. In life the body, when cleaned, is pale 
grayish, with an almost transparent integument, through which the 
convolutions of the dark intestine are conspicuous. 
Text-flg. 14. — Caesira papillosa (Verrill). X 4. 
"The largest specimens are about .40 of an inch in diameter." 
The largest specimen in the collections examined by the writer was 
14.5 mm. long, 9 mm. high, and about 7 mm. transversely across the 
body, but most of the specimens were of less than two thirds of these 
dimensions. The fact that even in a strongly contracted state the 
siphons, though much shortened, are not retracted, is somewhat 
characteristic of this species. In many individuals the siphons, 
though divergent, arise rather near together from a common base or 
low extension of the dorsal region of the body. Some of the specimens 
appear to have been attached to rocks, shells or other objects. 
Musculature of mantle weak and for the most part diffuse. Circu- 
lar and radiating bands about the bases of the siphons comparatively 
weak, and though numerous transverse bands are present in the region 
along each side of the endostyle they are very slender (usually only 
the width of three or four fibers). 
Tentacles of several sizes or orders arranged according to the usual 
scheme but not without some irregularities. Smallest ones un- 
branched, the others irregularly branched in a pinnate or more or less 
bipinnate manner. Tips of the branchlets ending bluntly, and often 
perceptibly swollen. 
Orifice of the dorsal tubercle longitudinally elongated and slit-like. 
Dorsal lamina a comparatively narrow membrane, smooth-edged 
