52 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
stricted, and in the granules being less developed on one side of the spine. 
In none of our specimens is a cup-like expansion of the distal end of the 
spine to be seen. 
Spines of Cidaris from the upper Cretaceous (C. dissimilis Forb., scep- 
trifera Mant., perornata Forb.) show some resemblance to our species, 
but they differ in the granules being larger, more remote, and forming 
more distinct rows. Also the general form is different, the cross section 
being round, and the spines being not regularly cylindrical, but more or 
less swollen near the base. 
Fain. ECHINID.E Wright. 
Gen. HYPECHINUS Des. 
2. Hypechinus patagonensis (d’Orbigny). 
Pi. XI, Fig-. 2. 
1842 Echinus patagonensis d’Orbigny, Voy. Amer. merid., v. 3, part 4, p. 
135, pi. 6, f. 14-16. 
1846 E. p. Agassiz and Desor, in: Ann. Sci. nat. ser. 3, v. 6, p. 370. 
1858 Hypechinus pat. Desor, Synops. Ech. foss., p. 130, pi. 18, f. 4. 
Test suborbicular, slightly subpentagonal, rather elevated. Interambu- 
lacral space with two vertical rows of primary tubercles, which are very 
prominent and distinct, differing considerably in size from the other tuber- 
cles. The latter (the secondaries) are small, numerous and unequal, 
irregularly scattered over each plate. Ambulacral spaces also with two 
vertical rows of tubercles, which, on the abactinal side of the test, are 
much smaller than those of the interambulacra, while, on the actinal side, 
they are about as large as those of the interambulacra. Poriferous zone of 
ambulacra narrow, pores arranged in arcs of three pairs on each plate ; 
plates very high, and pores quite remote from each other. On the abac- 
tinal system the madreporic plate is a little larger than the genital plates. 
Genital openings large, near the triangular point of the plate. Genital 
plates and madreporic plate with small secondary tubercles near the anal 
edge. All ocular plates separated from the anal system by the genital 
plates. 
Diameter of our specimen : 30 mm. 
