142 PEOF. p. M. Duncan's revision or the 



G-enus Pachtcltpeijs, Desor, 1858, Synopsis, p. 1Q8. Gotteau, 

 18G7-74, Fal. Frang., Ech. Terr. Jura, vol. ix. pi. 101. 



Test large, thin, ovoid in marginal outline, tumid above. 



Apical system compact ? 



Ambulacra flush, apetaloid, similar, becoming v^^ider towards 

 the margin and contracting towards the peristome ; pairs of pores 

 in simple series. 



Peristome central, in a depression, indistinctly decagonal. 

 Periproct supra-marginal and at the posterior surface. Tubercles 

 irregularly distributed. 



Fossil. Oolite : Europe. 



It is a very unsatisfactory genus and must be placed amongst 

 the doubtful series. 



Order IV. CLTPEASTEOIDA. 



The suborder Clypeastridse was, as A. Agassiz remarks in his 

 'Eevision of the Echini,' p. 504, limited by his father. The cha- 

 racters of the group are sufficiently determined in the 'Prodrome 

 d'une Monog. des Eadiaires,' 1836. But the morphology of the 

 suborder was accurately described by J. Mliller in his celebrated 

 work on the structure of the Echinodermata (" Bau d. Echino- 

 dermeu," Abhandl. d. konig. Akad. d. Wiss. Berlin, pub. 1854, 

 p. 123) ; and many very important points in the anatomy were also 

 explained by Loven, in his Etudes (Kongl. Svenska Vetenskaps- 

 Akad. Handl. Bd. si. no. 7, 1874, pp. 32 & 47). 



Loven recognized the name given by L. Agassiz and wrote 

 the first perfectly accurate and sufficiently synthetic definition 

 of the suborder {o]p. cit. p. 32). It was evident from the exam- 

 ination of the recent and fossil forms which should come within 

 the suborder that it would have to be split up into divisions of 

 greater or less distinctness, and the types of Clypeaster, Scutella, 

 Laganum, and FcJiinocyamus were noticed to present structural 

 differences of unequal, but still of definite classificatory value. 

 The question arose, were these types to represent families or 

 subfamilies, and if the latter, how many families were to be 

 recognized ? A. Agassiz, in his ' Eevision of the Echini,' divides 

 the suborder into two families each containing subfamilies, and 

 his first family is Haeckel's Euclypeastridse (G-enerelle Morpho- 

 logic, 1866). The subfamilies were Fibularina, Grray, for FcTiino- 

 cyamus and its allies, and the Echinanthinse for Glypeasters (A. 

 Agassiz wrote this last term with the family affix " idae "). Now 



