Dr, fourtau—LEchinid Fawna of the Neogene. 357 
The Gnathostomata are represented by forms belonging to the 
genera Echinocyamus, auct. (non Lambert), Scutella, Agassiz, Amphiope, 
Desor, and Clypeaster, Lamarck. Two forms, one Miocene, £. stellu- 
latus, Capeder, the other Pliocene, Z. puszllus, Miller, represent the 
first genus. The Scutelle are represented by six forms all peculiar 
to Egypt, the Amphiope by three species, of which one, 4. palpebrata, 
Pomel, is characteristic of the Burdigalian of Portugal and Algeria. 
Finally, the genus Clypeaster is represented by one Pliocene species 
and by eighteen from the Miocene. It is interesting to note that all 
the Miocene forms in Egypt are low or of very small elevation, and 
nowhere in this stage have those grand types of notable dimensions 
been met with so frequent in the Neogene of the Western 
Mediterranean, not only in Algeria, but also in Spain, France, 
Corsica, Sardinia, in Upper Italy, and more rarely in Malta. The 
presence in Egypt of depressed forms such as C. intermedius, 
Desmoulins, C. marginatus, Lamarck, and C. martini, Desm., or of 
moderately high ones such as C. crassus, Agassiz, C. scille, Desm.., 
and OC. subdecagonus, Peron & Gauthier, forms which are found in the 
western regions, forbids the hypothesis of difficulty or discontinuity 
of communication between the oriental and occidental basins of the 
Miocene Mediterranean, and the more so that with the Pliocene there 
appears in Egypt a representative of the group of C. altus, Klein, 
the C. egyptiacus, Wright, which is so polymorphic that certain of 
its specimens display the typical aspect of the ancestral form and of 
its variety, the C. portentosus, Michelin. We are therefore led to 
think that this absence of forms, with thick and very high tests in 
the Egyptian Miocene, is due to the composition of the waters and the 
littoral deposits of this sea, which did not contain sufficient carbonate 
of lime of the calcite type so assimilable as to permit the Clypeaster 
developing the plates of their test in sufficient thickness and the 
pillars of their endoskeleton destined to support the inflation of their 
_ambulacral rosette. 
The Atelostomata are as abundantly represented as the Gnathio- 
stomata, and by a larger number of genera. 
The Pliolampas, Pomel, are represented by three forms, of which 
one, P. welschi, Pomel, is known in Algeria. chinolampas, Gray, 
has twelve species, of which three, Z. plagiosomus, Agassiz, EH. monte- 
sinensis, Mazzetti, and £. pignatarii, Airaghi, belong to the Cono- 
clypeiform group; the others are all true Echinolampas with test of 
small elevation. One only, Z. hoffmanni, Desor, is Pliocene. 
The genus Pericosmus, Agassiz, is only represented by the typical 
species, P. latus, Agassiz, which is very abundant at several levels. 
The genus Brissopsis, Agassiz, is also only represented by a particular 
race of B. crescenticus, Wright, B. fraasi, Fuchs. There is only one 
representative of Agassizia, A. zitteli, Fuchs. The genus Opisaster, 
Pomel, is represented by two forms which appear to be successive 
mutations of the same type, O. lovisatoi, Cotteau, and O. almerat, 
Lambert. The specimens of Schizaster, Agassiz, are in general so 
badly preserved that it is only possible to mention two species with 
certainty, S. eurynotus, Agassiz, and 8S. legraini, Gauthier. The 
genus Zrachyspatangus, Pomel, is represented by 7. tuberculatus, 
