I860.] DUNCAX ECHINODERIIATA. 39 



1. Fs&udodiader/ia EuppeUi, Desor. Egypt. 



2. Heterodiade'/na libycirm, Ag. & Desor, sp. Egypt. Batna in Algiers; 

 Martigues, France. Zone of Ostrea columha. Martigues, France, below the 

 zone of Co.prina adversa. 



3. Hokcfypzis excisus, Desor, sp. Le Mans ; lie d'Aix. Zone of Turrilites cos- 

 t-atiis and T^ygurus lumpas. 



4. Periaster elatiLS, d'Orb. Le Mans ; Yvre I'Eveque. Zone of Ammonites 

 navicidaris. 



5. Hemiaster gracilis, Cotteau. Yvre TEreque. Zone of Ammonites navictu- 

 rnris. 



6. Epiaster dhtinctus, d'Orb. South-east Arabia, with Hemiaster similis 

 Cidaris cenomanensis and Tygaster trv.ncatus. Ireland ; Comes and Yilliers, 

 France. Zone of Pecten asper (upper part). 



3. List of the species already descHhed from Sinai : — 



1. Diplopodia Sinaica, Desor, sp. 



2. Clavias^er cornutus, d'Orb. 



3. Pedina &inaica, Desor. 



4. List of the species from South-eastern Arabia i — 



1. Cidaris cenor/ia?ie'nsis,Cottea.\i. Yvre rEreque. Zone of Scaphites esqualis. 



2. Pseudodiadema Eoemeri, Desor. Hildesheim. 



3. Salenia scutigera, G-ray. Warminster ; Le Mans. Zone of Scaphites 

 ^qualis. 



4. Holecfypus cenomanensis, Gueranger. Texas ; Le Mans. Zone of Pygurus 

 jas. 



5. Pygaster &iincaizis, Agassiz. North Ireland ; Condrecieux. Zone oi Pecten 

 asper. 



6. Epiaster distvnctus, d'Orb. Sinai; Ireland; Comes. Zone of Pecten 

 asper. 



7. Hemiaster si?nilis^, d^ Orb. Bagh; Le Mans. Zone of Am?nonites navi- 

 cular is. 



8. Cottaldia Garteri, nobis. 



ComMning, then, the Sinaitic and south-east Arabian Echino- 

 dermata, a fauna is produced "which is eminently characteristic of 

 the middle cretaceous horizon. 



5. Remarlcs on the species, their persistence aiul vaiiahility . — The 

 Holectypus from Sinai, formerly termed a Discoidea, is found in three 

 forms. One cannot be distinguished from the type of H. excisus ; and 

 the others are simple vaiieties, their size being the presumed varia- 

 tion. 



Periaster elatus is found as a slight variety, and Epiaster distinctus 

 also. 



The vertical range of Heterodiadema lihycum is worthy of notice, 

 because it resembles that of some of the South-east Arabian Echino- 

 dermata. The species lasted during the Hippuritic chalk age, as 

 well as during the antecedent Cenomanien. 



The comparative absence of species unknown in Europe is some- 

 wha tremarkable ; and so is the presence of some of the rarer Echino- 

 dermata of the well-searched French district of La Sarthe. It is 

 very interesting to discover that the majority of these wide-wander- 

 ing Echinodermata had a tendency to vary from their types, both in 

 Eiu'ope and in Arabia, and that the rest were persistent in form. 



In conclusion, I must refer to tlie remarks upon the diffusion and 



* M. Hebert determines this species to be identical with H. Leymeri. 



