466 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.45. 



STYELA MACRENTERON, new species. 

 Plate 34, Figs. 18-20. 



Superficial characters. — Large, specimens from 50 to 90 mm. in 

 length not uncommon, in general cylindric in form, the length from 

 two to three times the diameter. Usually attached by the whole 

 posterior end and rising column-lilvc. Smaller specimens more 

 nearly spherical, often in clusters, though less closely crowded than 

 some of the related species. Orifices at the anterior end usually 

 separated by a w^art-like or spine-like tubercle, the four distinct 

 lobes rather small; siphons not high in the preserved specimens, but 

 frequently rather tumid and conspicuous indicating that in life they 

 may be of good length; branchial frequently bent over so that its 

 orifice is directed ventralwards. Test thin and parchment-like, 

 rather easily torn smooth on the inner surface, but the outer surface 

 presenting a great number of nearly parallel circular ridges, sharply 

 defined, and giving the animal a very characteristic appearance; these 

 ridges more positively developed in older specimens. In addition 

 to the ridges the surface of the test bearing short, thick, somewhat 

 fleshy processes, in some specimens and in some areas of the surface 

 these being so close together as to give the appearance of the plush 

 of velvet. Occasional areas entirely devoid of either ridges or pro- 

 cesses the test then being left smooth and glistening. Barnacles, 

 hydroids, other ascidians, etc., frequently clinging to the surface. 

 Color light gray, frequently obscured, especially in the grooves between 

 the ridges, by dirt and other foreign substances. Mantle strong from 

 the heavy uniform layer of external longitudinal muscle fibers and 

 the somewhat less strong internal circular layer. 



Respiratory system. — Branchial tentacles varying from 40 to 65, 

 in a single circle, rather stout and crowded, of different lengths. 

 Dorsal tubercle prominent, the hypophysis mouth horseshoe-shaped, 

 the ends approaching each other closely and rolled in. Dorsal lamina 

 entire. Branchial membrane with four folds on each side, these not 

 high in proportion to the size of the sac as a whole; longitudinal ves- 

 sels on the folds crowded, from 10 or 11 to 22, occasionally more 

 (compare table), from 6 to 12 vessels between the folds; these not 

 crowded. From 4 to 9 stigmata to the mesh. 



Alimentary system. — On the left side, stomach very long and 

 relatively narrow, bent almost at a right angle near its esophageal 

 end, its posterior two-thirds or three-fourths standing nearly erect 

 and reaching from the very base of the body to above its middle, 

 it bemg thus more than half the length of the animal. The stomach 

 wall with from 25 to 50 prominent internal longitudinal folds, these 

 being visible on the external view of tlte organ. Intestine remark- 



