ENCOPE EMARGINATA. 325 



Encope emarginata 



Echinodiscus emarginatus Leske, 1778. Kl. Add. 

 ! Encope emarginata Agass. 1841. Mon. Scut. 



Pi. XII. f. u-Us PI- XII"  /■ is; PI XII". f. 2-3. 



As the accompanying measurements show, it is difficult to define the out- 

 line of this species, its variations including all possible forms between a 

 more or less pentagonal outline with the deep cuts (lunulas) at the .angles 

 of the pentagon, and a subcircular outline anteriorly, retaining only one 

 side of the pentagon posteriorly. Seen from above, denuded of spines, the 

 whole test is covered by remarkably uniform tubercles closely packed with 

 extremely diminutive miliaries, the same granulation extending over the 

 ambulacra, both the poriferous zone and the median part of the rosette; only 

 on the edge of the lunules do we find somewhat larger tubercles. As in 

 other Scutellidae, the median interambulacral spaces are covered by larger 

 tubercles, as well as the rest of the lower surface, except in the proximity 

 of the ambulacral furrows and their branches, which form broad avenues 

 covered by small miliaries. In the typical E. emarginata the lunules are 

 more or less elliptical, and usually their edges at least touch, if they are not 

 completely closed ; the odd interambulacral lunule is nearly twice as long 

 as any of the others ; the edge of the test in such specimens is thin, and 

 the outline in profile is gradually sloping from the vertex to the ambitus. 

 The vertex is eccentric anteriorly, and corresponds usually also with the 

 apex ; but it is not unfrequent that the anterior edge of the posterior lunule 

 is slightly higher, especially if the lip of the lunule is well developed, as 

 in the case of what has been called Encope oblonga, where the lunules are 

 completely closed, and the edge of the test and of the lunules is thick, the 

 outline beinsr at the same time somewhat circular. When the lunules 

 remain wide open, and the general outline of the test is pentagonal, it 

 has received the name of E. Valenciennesii, but there are no features 

 by which it can be separated specifically ; though there is a species on 

 the west coast of America having very much the same general outline 

 (E. grandis), which has, however, such remarkable internal structure that 

 there are excellent grounds for maintaining that species. 



In specimens measuring 13. n "" in diameter, the ambulacra are not yet 

 separated from the digestive cavity by the complete wall of spongy calca- 

 reous mass so prominent in old specimens. In these and young specimens 

 simple pillars connect at first the two floors, as in Mellita and Echinodiscus. 



