ON SOME PLYMOUTH HOLOTHURIANS. 



213 



Cucwnaria saxicola B. and R. 



Surface spicules of body irregular 

 in shape, consisting of rods radiating 

 from a central portion, scattered in 

 the skin. (See I.e. above and also 

 Fig. 6, p. 221.) 



Podial spicules have foramina 

 typically in a single series. (See 

 Fig. 6, p. 221.) 



Gonadial tubes relatively few. 

 varying in number between 10 and 

 about 60, large, and club-shaped. 

 (See Fig. 1, p. 214.) 



Calcareous collar relatively deli- 

 cate. Interradial calcareous pieces 

 deeply bifurcated posteriorly. (See 

 Fig. 4, p. 218.) 



Dorsal ambulacra with modified 

 tube-feet. (See Fig. 9, p. 228.) 



Spawning period about May. 



Cucumaria normani Pace. 

 Surface spicules campanulate, 

 forming a continuous covering in the 

 skin of the body. (See Figs. 8 and 7, 

 pp. 225 and 222.) 



Podial spicules have foramina 

 in two or more parallel rows or with 

 a group of 3 or 4 small foramina at 

 each end of the spicule. (See 

 Fig. 7, p. 222.) 



Gonadial tubes very numerous, 

 frequently more than 500, relatively 

 small, and of even cylindrical calibre. 

 (See Fig. 2, p. 214.) 



Calcareous collar relatively strong. 

 Interradial calcareous pieces only 

 slightly bifurcated posteriorly. (See 

 Fig. 5, p. 219.) 



Dorsal ambulacra with ordinary 

 ambulatory tube-feet. 



Spawning period about March. 



The differential characters of most importance in the foregoing table 

 are (1) those of the main body spicules, (2) the spicules near the surface 

 of the body, (3) the shape and number of the gonadial tubes, and 

 (4) the shape and relative stoutness of the pieces of the calcareous collar. 

 Pace has already emphasized the first and second of these characters. 

 These have, however, gained additional importance from the recent 

 observation of their correlation with differences in the gonad and cal- 

 careous collar. In C. saxicola the gonadial tubes are large, club-shaped, 

 and few in number (see Fig. 1, p. 214), while those in C. normani are 

 relatively small, of even, cylindrical calibre, and very numerous, (See 

 Fig. 2, for the faithful drawing of which I am indebted to Mrs. Orton, 

 as well as for all the figures by which this paper is illustrated.) The gonad 

 in the male and female in each of these forms is alike in its structure. 

 The eggs of both species are about the same size, i.e. about -4 mm. in 

 diameter, but the sperm has not been examined closely. 



