MELLTTA STOKESII. 5?7 



species of Mellita. The mere fact of the lunulea remaining open so fre- 

 quently, the position of the posterior lunule, and the comparatively greater 

 size of the petals are not sufficient grounds, now that we know the changes 

 due to growth in three of the species of Mellita, to separate this species 

 from Mellita and unite it with Encope. We find in M. longifissa, where we 

 have but five lunules, the extreme development of the posterior ambulacral 

 petals so characteristic of the species of Encope. A large series of speci- 

 mens shows that the closing of the lunules takes place as in Mellita penta- 

 pora, and not by perforation as in M. hexapora, to which it is apparently most 

 closely allied. 



The outline of this species is more circular than any other of the genus, 

 less truncated posteriorly ; the divergence of the petals is quite regularly 

 pentagonal ; the petals are of nearly the same length ; the odd anterior 

 petal somewhat the longest. The apical system is eccentric posteriorly. 

 The apical system is prominent, with five large genital openings. The pos- 

 terior opening is less prominent, scarcely perceptible sometimes, and more 

 or less irregular. 



The petals are broad, rounded at extremity, which is quite distant from 

 the lunules. The posterior lunule is rounded, placed near the edge, within 

 the inner extremity of the posterior pair of lunules. The ambulacral lunules 

 are frequently open, as in Encope, barely closed, or completely soldered, as 

 in the other species of Mellita. 



The actinostome is pentagonal, not central, near posterior edge ; anus is 

 pyriform, placed half-way between the edge of the test and mouth. Main 

 ambulacral furrows well marked. Tuberculation of lower surface has 

 general features of Encope. The tubercles of the lateral posterior interam- 

 bulacra are large, of uniform size, closely packed ; those of the other interam- 

 bulacral spaces are large and distant near the actinostome, but diminish 

 rapidly in size towards the edge, where they are very small and closely 

 crowded together. The tuberculation of the abactinal surface is uniform in 

 size, closely crowded. The spines of the abactinal surface are uniform in 

 size, slender, clavate, cylindrical near the edge, more or less crowded accord- 

 ing to the tuberculation ; while on the lower side they are larger and 

 stouter in the median interambulacral and ambulacral spaces. The small 

 actinal tubercles of both areas carry minute spines, resembling those of the 

 upper side, more slender, however, and less clavate. Greatest width of the 

 test slightly behind the central transverse axis. Dried specimens are green- 

 ish-brown ; in alcohol more olive-colored. 



