326 ENCOPE EMAEGINATA. 



PI. XII'. f. .' shows the extent t<> which the ambulacra are isolated from 

 the remainder of the digestive cavity in fully grown specimens. The jaws 

 are quite small (PI. XIP. f. ,;), and the calcareous cellular work connecting 

 the two floors leaves a comparatively small space for the winding of the 

 alimentary canal, which becomes quite narrow and small by the time it 

 reaches the anal opening. 



Among the specimens dredged from considerable depth were a number of 

 Encope emarginata of various sizes, from half an inch in longitudinal 

 diameter to an inch. These, in addition to a large series of young of the same 

 species sent from Desterro by Dr. Fritz .Midler, present some interesting 

 structural points, and have also, not unexpectedly, however, led to the con- 

 clusion that Moulinsia was nothing but a young Encope. Dr. Liitken, in 

 speaking of the chance of young Encope being a Moulinsia. seemed to con- 

 sider the scalloped v^\^e as a most distinguishing feature. The same fea- 

 ture is also quite prominent in young Mcllita. but they are always more 

 circular, and do not assume the elongated form which is so characteristic of 

 Moulinsia. This scalloped edge is not most prominent in the youngest 

 specimens; it is mosi striking when they are from 6.°"" to N.""" in diameter. 

 previous to the appearance of the lunules on the dorsal side, when, as 1 

 think, the figures will show plainly they have all the appearance of Mou- 

 linsa (PI. XII. f. /;, /:.). There are some points in the structure of the 

 young specimens of the size figured by Liitken. to which it may he worth 

 while calling attention. Liitken has noticed that there was a striking differ- 

 ence in .Mcllita and Encope in the modes of formation of the ambulacra! 

 lunules. In Encope they are formed by the closing in of notches made by 

 the prolongation of the plates, which often remain open during the whole 

 life, while in Mellita (M. sexforis) the ambulacral lunules are formed by pits 

 in the test itself. I have noticed that these pits (lunules) appear al first on 

 the lower surface, and little by little force their way through the test (see 

 Mellita sexforis); the posterior interambulacral lunule in Mellita is formed in 

 the same way, and the same is the cast' in Encope, where I have observed it 

 in the youngest Encope (a specimen from Desterro. sent by Dr. Fritz .Midler) 

 in the condition of a Moulinsia. when the lunule was a very marked pit on 

 the lower surface alone (PL XII. f. 15), not yet having forced its way through 

 the test to the dorsal side, which had a smooth unbroken posterior inter- 

 ambulacral doi-sal area (PI XII. f. 1.',). The anus opens directly in the 

 centripetal extremity of the lunule, while in the adult the lunule and the 



