Mr, F. M‘Coy on some new Paleozoic Echinodermata, 258 
Russia and the Ural Mountains. Under those circumstances, 
therefore, it seems the most simple and correct course to use the 
ia term Archeocidaris for those fossils. 
The order Perischoechinida may be divided into two families : 
Ist, Palechinide, having the interambulacral plates crowded with 
small, subequal, spinigerous tubercles, not perforated, the spines 
of one form (including Palechinus, Melonites, Owen and Nor- 
wood, &c.); 2nd, Archeocidaride, having the spines and tubercles 
of two forms and sizes, the primary spines very large, generally 
muricated, crenulated at the base, and each supported on a large 
mammillated and perforated primary tubercle surrounded by an 
elevated ring, never more than one on any plate, generally sur- 
: rounded by a crowd of the small secondary tubercles (including 
a Archeocidaris, M‘Coy, and the following). These family divi- 
____ sions rest on the same characters as the separation of the true 
. Echini and the Cidaride among the normally formed Echinida. 
Perischodomus (M‘Coy), n. g. 
Etym. wepicxe@v, complexus, and daua, domus. 
Gen. Char. Spheroidal, depressed, subpentagonal ; ambulacra 
narrow, of two rows of small plates, most usually of a trans- 
oo o Oo 
° 99? 
o c 
(3) ; 
eG °¢o 
a. Diagram of portion of interambulacrum and ambulacra of Perischodomus. 
b. ait: of the primary and some of the secondary tubercles magnified more 
ighly. 
ce. One of the ovarian plates. 
versely elongate pentagonal figure, and each pierced by one 
pair of simple pores; interambulacra wide, of five rows of 
plates very irregular in size and shape, all the plates covered 
with small equal granules or secondary tubercles, while the 
row on each side adjoining the ambulacra alone bear the small, 
smooth primary spmes, one on each, the supporting tubercle 
being small, mammillated, perforated, but not crenulated, sur- 
rounded by a double ring and situated not in the centre, but 
near the ambulacral edge, a little above the middle; ovarian 
