228 PBOP. p. M. Duncan's t^evision oe the 



In the Eeport on the ' Challenger ' Echini, 1881, p. 182, A. 

 Agassiz united the species Tripylus cavernosus and T. australis, 

 and absorbed them and Ahatus PUlippi, Loven, in the genus 

 Hemiaster; he noticed that in a full-grown specimen of the spe- 

 cies " cavernosus " he could not find an anal fasciole. That was 

 in accordance with Troschel, but in young specimens distinct 

 anal fascioles joined to lateral ones existed, whilst in still larger 

 tests the lateral fasciole had disappeared, the linear subanal 

 remaining (p. 177). 



The sex has much to do witb the variation in structure of the 

 apical system, and the number of pores is two or three ; the 

 female which was drawn (pi. xx«. fig. 19) had two genital pores 

 only, the males bave three. 



In ' Pourtalesia,' 1883, p. 72, Loven holds his ground with, re- 

 gard to the generic value of Abatus, and attributes it to Troschel. 

 Certainly Abatus was a section of Tripylus according to Troschel. 

 Loven gives the synonymy of the species " cavernosus " and 

 " australis,''' and it is interesting to observe that he is alone in the 

 employment of the term Abatus. But although there may be a 

 difference of opinion regarding the classification employed by the 

 illustrious Professor, everybody must admire and be thankful for 

 the anatomy given by him of the young " cavernosus^'' whatever 

 its correct generic name may be, in which he indicates a fifth 

 basal plate placed between the posterior radial plates and bearing 

 the madreporite. Moreover, he has shown how homogeneous a 

 group the ethmophract species of Hemiaster are, and that to 

 introduce the others within the same category would violate 

 the simplicity of the genus as established by Desor. But it 

 must be conceded that Loven's teaching infers evolution of the 

 ethmolysiau from the ethmophract " calyx," and if the modern 

 species of Hemiaster of the first group are the descendants of 

 the ancient ethmophracts, surely it is a reason for preserving 

 the genus with necessary modifications. 



After what has been written, it appears necessary to absorb 

 Abatus in Tripylus as a subgenus of Hemiaster. The attempt to 

 divide the genus Hemiaster by grouping the species with four basal 

 plates, each perforated, and having the madreporite separating the 

 postero-lateral basals, under the genus Tecchy aster, Pomel, will 

 fail amongst the students of the recent fauna. The distinction 

 is specific, and the so-called genus lapses. Bitremaster of M- 

 MuDier-Ciialmas (1885, Compfc. Eend. Acad. Sci. 2 semestre, 



