H. L. Haivkins — Eckinoidea Holectyjpoida. 399 



that morphogenesis may be not merely parallel in otherwise 

 divergent stocks but proceeds at the same rate. Hence come 

 " modes " or " fashions " prevalent in ultimately homogenetic 

 series — sources of convenience to the stratigrapher and confusion 

 to the systematist. 



4. The Affinities of Echinolampas. 



H. L. Clark (Haivaiian and other Pacific Echini, p. 143), com- 

 menting on my suggestion that the " Nucleolitidae " (i.e. the 

 Cassiduloidea of Sladen and Asternata of Gregory) may be 

 diphyletic, states that " the recent species seem to form a very 

 homogeneous group " ; but he admits that " a more natural grouping 

 in accordance with some of [my] suggestions " may prove possible. 

 The earlier sections of this paper seem to me to show that Apatopygus, 

 at least, is a very distinct type from the Oligopodia-Rhynchopygns- 

 EcMnolampas series of recent Cassiduloids. Ap)atopygus has 

 definitely dissimilar petaloid pores — those of the Cassiduloida are 

 similar and normally conjugate. I have no knowledge of any other 

 living genus that can be associated with Apatopygus in the 

 Nucleolitoida, and so agree with Clark as to the apparent 

 homogeneity of his Nucleolitidae with this single exception. 



In several of the papers in this series, and especially in my recent 

 memoir on ambulacra (Phil. Trans.), I have argued that the 

 Echinolampas-seiies (which I call Cassiduloida sens, sir.) are 

 sequentially related to the early Echinoneidae much as the 

 Clypeastroida are to the Discoidiidee. In the almost complete absence 

 of knowledge of post-larval changes in recent Echinoids (zoologists, 

 please note !), my arguments have necessarily been somewhat 

 hypothetical or based on unverified assumptions. But in the 

 section of Agassiz' Revision " On the young stages of Echini " 

 (Part IV), p. 741, and in the plate (xvi) illustrative of the particular 

 paragraph, something approaching ontogenetic proof of my con- 

 tention appears. Agassiz says : " The development of Echinolampas 

 has thrown unexpected light upon the affinities of the toothless 

 Galerites and of the Cassidulidse. It shows conclusively that 

 Echinoneus is only a permanent embryonic stage of Echinolampias, 

 thus becoming allied to the Cassidulidse, and that it has nothing in 

 common with the Galerites as I would limit them, confining them 

 entirely to the group provided with teeth." These sentences were 

 written long before Agassiz was able to record the presence of a 

 vestigial lantern in young Echinoneus — in the light of that discovery 

 the genus has almost everything " in common with the " 

 Holectypoida. Study of Agassiz' drawings (pi. xvi, figs. 1-3) shows 

 that Echinolampas depressa, when 4 mm. in diameter, is more like 

 a Conulus or " Glohator " than an Echinoneus in general facies, but 

 has the tuberculation of a Discoidea. At a later stage, 12" 7 mm. in 

 diameter (tab. cit., figs. 8-10, here partly adapted, PL VII, Fig. 5), 

 the test takes on a more depressed and elongate form, and the 



