212 J. H. ORTON. 



denied that these two forms were different, so that the literature on 

 them was left in an unsatisfactory state. On investigating these two 

 forms, however, I have obtained sufficient evidence — from the characters 

 of the gonadial tubes, the calcareous collars, and the young of both forms 

 — to verify the observations of Pace and to meet satisfactorily the 

 objections put forward by Norman against them. The differential 

 characters of these two species as given by Pace (loc. cit.) have been 

 verified in an unpublished investigation by Mr. W. De Morgan and by 

 the present writer. These characters, most of which were observed by 

 Pace, are now given revised * in the following table in a comparative 

 manner, so that the differences between these two species can be readily 

 shown : — 



Table 1. — A comparison and a contrast of the characters cf C. saxicola 



Brady and Robertson and C. normani Pace. 



Cucumaria saxicola B. and R. Cucumaria normani Pace. 



f Common on the shore, also taken f Fairly common on the shore, also 



in depths of a few fathoms. taken in depths of a few fathoms. 



General colour of body a pure General colour of body dirty 



milk white, becoming black when brownish white, becoming black 



exposed to light. when exposed to light. 



Surface of body smooth. Surface of body much wrinkled. 



Body wall delicate, relatively Body wall tough, coriaceous, 



thin, marked only with transverse crowded with spicules, 

 strise due to encircling fibres of the 

 superficial muscle layer, with rela- 

 tively few spicules. 



General body spicules devoid of General body spicules typically 



nodulation, lozenge-shaped in one lozenge-shaped, perforated with four 



stage of growth, but subsequently large foramina, and always bearing 



developing 2 or even 3 additional- on each side about 12 very prominent 



foramina on the ends of the spicule nodules. (See 3, Plate XI, Fig. 1.) 

 and thus losing their lozenge shape. 

 (See 4, Plate LXXII, Fig. 3.) 



* Owing to the fact that both species develop black pigment when and where exposed 

 to light, it follows that the differential characters depending upon the degree of pig- 

 mentation of the tentacles and anal aperture noted by Pace cannot be relied upon, and 

 have consequently been abandoned. 



t As an example for illustrating the occurrence of these two forms, in one day's 

 collecting on the shore (3rd April, 1911, Wembury Bay) about 80 C. saxicola were obtained 

 and only about 6 C. normani, including specimens of various sizes. Another day (1st May, 

 1911) about 40 C. saxicola were obtained and only 2 C normani. This disproportion is 

 usual in this district. 



