[ 211 ] 



On Some Plymouth Holothurians. 



By 



J. H. Orton, A.R.C.Sc, B.Sc, 



Naturalist at the Pli/inotith Laboratory. 



With 13 FiKuies in the Text. 



TABLE OF CONTENTS. 

 PART I. 



On the specific characters of Cucumaria normani Pace, and Cucumaria saxicola 

 Brady and Robertson, with an account of some undescribed differential 

 characters and an investigation of the variation of the gonad in C. saxicola 

 Comparison of the characters of C. normani and C. saxicola . . . .211 



Variation of the gonad of C. saxicola . . . . . . . .214 



The gonad of C normani . . . . . . . . . .217 



Characters of the calcareous collar of C. 5rt.r(co/a and of C ?ior/««?n' . . . 219 



Characters of the spicules and tube-feet in C. saxicola and C. normani . . . 220 



Discussion of some former observations on C. saxicola and C. normani . . 222 



The growth-stages of the bell-shaped spicules of C. normani .... 224 



The synonymy of C. saxicola Brady and Robertson and of C. normani Pace . 225 



Correlation in the characters of the gonad and ambulacra in the genus Cucumaria 228 



PART II. 



On the occurrence of Cucumaria elongata Diib. and Kor. and Thijone raphanus Dlib. 



and Kor. in the Plymouth District ........ 229 



Notes on Cucumaria elongata .......... 230 



On Thyone raphanus Diib. and Kor. ........ 232 



PAET I. 



ON THE SPECIFIC CHAKACTERS OF CUCUMARIA NORMANI 

 PACE, X^B CUCUMARIA SAXICOLA BRADY AND ROBERT- 

 SON, WITH AN ACCOUNT OF SOME UNDESCRIBED DIF- 

 FERENTIAL CHARACTERS AND AN INVESTIGATION OF 

 THE VARfATION OF THE GONAD IN C. SAXICOLA. 



COMPARISON OF THE CHARACTERS OF C. NORMANI NSD 



C. SAXICOLA. 



Some of the specific and differential characters of these two species have 

 already been enumerated by Pace (1). Subsequently Norman (2) 



NEW SEIIIES.— VOL. X. XO. 2. JUXE, 1914. o 



