LYTECHINUS ANAMESUS. 255 



pore near the "distal tip, while on the proximal margin it carries a secondary 

 tubercle. There may be one or rarely two other tubercles on the plate but 

 otherwise its surface is quite smooth. The madreporic genital is conspicuous, 

 with a large group of pores. The ocular plates are large and each carries at 

 least one secondary and a number of miliary tubercles. The pore is evident 

 near the distal margin. Of fifty specimens examined, all exceeding 15 mm. h. d., 

 19 (38%) have no oculars insert, 17 (34%) have ocular I insert, 11 (22%) 

 have oculars I and V, while 3 (6%) have ocular V only. Of the ten largest 

 specimens, three have no oculars insert, three have I, three have I and V, and one 

 has V alone. Where such diversity is shown, it is clear that the oculars do not 

 furnish a very helpful specific character. 



The interambulacral plates at the ambitus are low, the width exceeding twice 

 the height. Each plate carries a conspicuous primary tubercle, which, at and 

 below the ambitus, is accompanied by two or three secondaries and several 

 miliaries; one of the secondaries is sometimes almost as large as the primary. 

 Above the ambitus, there are few secondaries and only scattered miliaries, and 

 the uppermost half dozen plates have their inner ends noticeably smooth and 

 bare. The ambulacral plates are relatively higher at the ambitus than the 

 interambulacral. The arrangement of their tubercles is essentially the same, 

 so that, while the test is well covered with tubercles actinally, there are ten 

 distinct, bare, areas abactinally, radiating out from the periproct. The am- 

 bulacra are relatively wide, about four fifths as wide as the interambulacra, at 

 the ambitus. The pore-pairs are in distinct arcs of three and as the pores are 

 large, the poriferous areas are relatively broad. 



The buccal membrane (PI. 99, fig. 4) is heavily plated, especially in the young; 

 in some adults, the distal plates show indications of resorption and the membrane 

 is occasionally visible between them. The primordial ambulacral plates are 

 much larger than any of the others and form a well-spaced ring. They carry 

 pedicellarise, as do some of the larger plates distal to them. The gill-cuts are 

 fairly well defined but are not deep. 



The primary spines are of variable length but are quite conspicuous. They 

 are longest at the ambitus, where their length may nearly equal the diameter 

 of the test. They are slender and taper very gradually from the low, incon- 

 spicuous milled-ring to the rather blunt point. Secondaries and miliaries are 

 similar, save for their much smaller size, but they are not abundant anywhere. 



Pedicellarise of all kinds are abundant but are not especially distinctive. 

 The globiferous have valves about .60 mm. long, of which the base is about one 



