Studies on the Echinoidea Holectypoida. 215 



The next stage was spent in comparison of the new type with 

 Mcsodiadema. At first the nature of the surface-ornament afforded 

 the best basis for this comparison ; but gradually all of the visible 

 features (except the periproct) came into line, until the Persian 

 form proved nearer to Mesodiadema than to Loriolella, with the 

 reservation just made. 



The last stage in growth of my opinion on the* problem opened 

 in bewilderment. Lambert & Thiery's " Essai de Nomenclature ", 

 fasc. iii, 1911, came into my possession. Mesodiadema and Loriolella 

 occur there on the same page in direct sequence, thus confirming 

 my use of both genera for comparison ; but Loriolella seemed trans- 

 formed ! In a previous paragraph I have shown the apparent reason 

 for this transformation ; but there remained the greatest stumbling 

 block of all. Loriolella had become a Regular Echinoid ! The 

 revised diagnosis, apart from its context, had almost succeeded in 

 restoring my first opinion — the Kelat forms represented a new 

 species of Loriolella ! But the last sentence in Lambert's account 

 — " L'un de nous a constate que le periprocte ne s'ouvrait pas hors 

 de I'apex " — sent me back to the better of the specimens to find 

 if I had been deceived. The region of the periproct was developed 

 further, even to the point of etching with acid, and examined wet 

 and dry, with naked eye, lens, and microscope, directly and in 

 photographs, and (most important of all) with half-conscious 

 exjyectation of finding a narrow genital, or its scar, enclosing the 

 aperture. But I am absolutely convinced that no such plate 

 exists, and that no such plate existed (unless in earlier ontogenetic 

 stages) in the new type. The periproct extends backward farther 

 than in any species of Pygaster ; the apical system, though 

 practically invisible, must have been quite large, and its site is 

 clearly indicated ; the coronal plates curve towards the periproct 

 exactly as in Pijgaster or the Nucleolitidae ; and I have no hesitation 

 in placing the Persian forms among the Echinoidea Exocycloida. 



In spite of their great resemblance to Mesoddadema and Loriolella, 

 they cannot find a home in either of those Endocyclic genera — 

 they are not Pygaslers (nor, indeed, Holectypoids), and there is 

 certainly no other Irregular genus into which they could be forced. 

 Their affinities will be discussed later ; but their difference from 

 all known types is of such a nature that a new genus, and even a 

 new family, are needed to give it expression. 



(ii) Diagnoses and Description. 

 PsEUDOPYGASTERiD^ Fam. nov. 

 Euechinoidea, Irregularia, ? Nucleolitoida, of subglobose form 

 and subpentagonal ambital outline. Apical system almost unknown ; 

 apparently large and eccentric posteriorly. Peristome pro- 

 portionately mmute, practically central, with ? feeble branchial 

 incisions, but no perignathic girdle (hence edentulous ?). Periproct 

 very large, posteriorly exocyclic, on the adapical surface, probably 



