164 THE .VOYAGE OF H.M.S. CHALLENGER. 



step is the appearance of a limited subanal fasciole or of a subanal fasciole with anal 

 branches ; something like this we find in .Homolamjxis. In Homolampas fragilis we 

 have an indistinct anal fasciole branching from the subanal fasciole, the peripetalous 

 fasciole evidently developing only at a late stage. This genus has on the whole more 

 important embryonic features than other Spatangoids of which the development is known; 

 Hemiaster and Schizaster, it is interesting to note, show quite a marked difference in the 

 appearance of the fascioles if we can judge from the two species of Hemiaster thus far 

 discovered. Yet while in the genus Homolamjoas the structure of the ambulacra show 

 such embryonic features as to connect it with some of the most typical of the Cretaceous 

 Echinoderms, there are other features which in their turn give it a most modern facies. 

 These are the highly specialised subanal fasciole, the compact abactinal system which 

 the genus has in common mth Pcdeopneustes, Linopneustes, Argopatagus, and other 

 Spatangina not possessing petaloid ambulacra ; the development of its primary tubercles 

 as in Lovenia, and the well-defined actinal plastron and specialisation of the tubercles of 

 the actinal surface. The resemblance of the miliary tuberculation of Homolampas fidva to 

 that of Spatangus loncophorus, Meneg., figured by Dames (1877, Palaeontog., vol. xxv., 

 pi. ix. fig. 6), is very remarkable, and were it not for the singularly well-developed 

 petaloid ambulacra of the Tertiary species, we could most readily assign it to the genus 

 Homolampas from the outline of its test, as the delicate peripetalous fasciole would very 

 easily escape notice unless the specimens were in an extraordinary state of preservation. 

 Unfortunately, nothing is knowTi of the structure of the actinal sm-face of that species. 



Argopatagus and Homolampas agree in having a flattened test, a labiate actinostome, 

 and a well-developed subanal fasciole, and in having the typical Spatangoid embryonic 

 ambulacra such as are characteristic of the Cretaceous genera Holaster and Cardiaster and 

 other Ananchytidse ; while in Genicopatagiis, with which both Argoj)atagus and Homo- 

 lampas are closely allied, the outline of the test resembles to a remarkable degree that of 

 Holaster and its allies. 



* Homolampas Julva (Pis. XXIV., XXXVIII. fig. 26). 



Homolampas fulva, A. Agassiz, 1S79, Proc. Am. Acad., vol. xiv. p. 209. 



Although this is a gigantic species compared to the small Homolampas fragilis which 

 I described from among the Echinids dredged by Mr Pourtales in the Straits of Florida, I 

 do not hesitate to refer it to the genus Homolamptas in spite of the very rudimentary 

 petaloid structure of the abactinal part of the lateral ambulacra. This species has all the 

 other features characteristic of the genus, such as the slightly sunken anterior ambula- 

 crum, the deeply indented test at the edge of the anterior extremity, the very elongated 

 lateral posterior ambulacra, the presence of a subanal fasciole, the position of the anal 

 system, and of the actinostome, the structure of the actinal surface, and especially the pre- 

 sence of huge primary tubercles like those oi Lovenia in the abactinal part of the interambu- 



