CHAETODERMA ERUDITA. 59 



taining in favorable preparations groups of small prismatic crystals. This 

 description answers for the present species with the exception of the crystals 

 which have not been found. Wiren compares this glandular area with the shell 

 gland of the Neomeniidae, though claiming it acts as an excretory organ. Be- 

 3'ond certain histological resemblances there are no cogent reasons for accepting 

 such a theory. 



Chaetoderma erudita, sp. nov. 



Ten specimens of this species were taken in Lynn Canal, Alaska (Sta. 4258) 

 at a depth of 300-313 fathoms; and forty-one were dredged in Chatham Strait, 

 Alaska (Sta. 4264) at a depth of 282-293 fathoms. In both cases the bottom 

 consisted of very tenacious green mud. A number of individuals were kept in 

 an aquarium aboard ship and lived apparently in a normal state, burrowing 

 extensively and in some instances feeding on organic debris. Two males gave 

 off considerable quantities of sperms during a period of over an hour. It escaped 

 from the sides of the cloacal cavity, lateral to the gills and soon diffused into the 

 surrounding water. Much care was taken in the preservation of these animals, 

 and yet the shrinkage was considerable, in the case of some of the more active 

 ones, amounting in six individuals to a decrease in the body length of one fourth. 

 It thus becomes apparent that the length index or ratio of length to diameter 

 is not to be depended on in the discrimination of species. 



The entire animal is represented (Plate 4, fig. 9) ; the buccal plate (Plate 4, 

 fig. 11), and the spicules (Plate 37, fig. 15). The hypodermis comprises three 

 fairly distinct ty])cs of cells. Of these the most conspicuous, in alcohol killed 

 material, is the basal cell of each spine whose nucleus is placed considerably 

 above the level of the other types. In material killed in vom Rath's fluid the 

 Reizenzcllen of Wiren, well-defined globular cells, are very distinct and con- 

 tain a highly vacuolated material which almost totally disappears in alcohol 

 killed specimens. In some cases fibres, probably muscle, attach to these ele- 

 ments as in C. altenuata, but (heir relations are difficult to determine. The 

 remaining cells are simple low columnar elements of the usual appearance. 



The mouth, a relatively wide opening in the deeply cleft buccal plate, opens 

 into a laterally compressed buccal tube that beneath the brain develops longi- 

 tudinal folds and a more circular outline (Plate 29, fig. 4). As far as the forward 

 end of the radular supports buccal glands in great abundance are attached to 

 its walls. The subradular organ is not as sharply defined as in C. attenuata, 

 yet is clearly distinguishable as a median ventral elevation composed of slender 



