NO. 3 CASSIDULOID ECHINOIDS — KIER II7 



is very large relative to the size of the test. The test of E. lehoni 

 is very high as is also the young test of E. fraasi. P^urther charac- 

 ters in E. lehoni also found in the young of E. fraasi are the large 

 subpentagonal peristome, larger periproct, large tubercles, and slight 

 crowding of pores in the phyllodes. The absence of petaloid pores 

 in ambulacrum III and the anterior poriferous zones of petals II and 

 IV also reflects the immaturity of the specimen of E. lehoni. In an 

 adult of Echinolampas there are usually less pore pairs in petal III 

 and the anterior poriferous zones of petals II and IV. Since any 

 inequality in the number of pore pairs must date back to the first 

 appearance of the pore pairs, there must be a period in the early 

 growth of an Echinolampas when there are no pore pairs in petal III, 

 and none or few in the anterior poriferous zones of petals II and IV, 

 after they have already begun to be formed in the posterior porifer- 

 ous zones of petals II and IV. Such is the case in E. lehoni, and 

 such was the case in E. fraasi. 



Specimens of Echinolampas affinis are very common at the same 

 locality where the holotype of E. lehoni was collected. It is probable 

 that E. lehoni is a young E. affinis, as both have the same shaped 

 petals with petals II and IV curving anteriorly, and similarly shaped 

 periproct and peristome. I have seen only a few specimens of E. 

 affinis, however, and hesitate to make E. lehoni definitely a synonym 

 of E. affinis without having studied a growth series. 



Genus PLESIOLAMPAS Duncan and Sladen 



Plcsiolampas Duncan and Sladen, 1882. Pal. Indica, ser. 14, vol. i, p. 9. Type 



species by monotypy, Plcsiolampas elongata Duncan and Sladen. 

 Synonym : Oriolampas Munier-Chalmas. 



GENERIC DESCRIPTION 



Medium to large size, elongate, low, apical system monobasal ; 

 petals long, open, narrow poriferous zones, of unequal length in 

 same petal ; single pores in ambulacral plates beyond petals ; periproct 

 inf ramarginal, longitudinal ; peristome transverse ; bourrelets well 

 developed, phyllodes single pored, with slight crowding of pores; 

 buccal pores present ; tubercles on adoral surface approximately same 

 size as on adapical. 



Comparison with other genera. — This genus is most similar to 

 Echinolampas having similar petals, bourrelets, phyllodes, and tuber- 

 culation, but differing in having a longitudinal periproct. 



Remarks. — I was unable to study any specimens of the type species 



