File:The Quarterly journal of the Geological Society of London (14073297792).jpg

444 PE.OP. p. M. DUNCAN 02f THE STETJCTITRE OP
(Echinides du Depart, de la Sarthe, par Cotteau et Triger, 1859,
plate xxxiv. fig. 5), the propriety of calling the species a I)i_plopodia
is doubtful ; for the pairs of pores resemble in their arrangement
those of Pedina.
The genus CypTiosoma, Agass., is characterized by the doubling of
the pairs of pores near the apex ; and this character is certainly
developed with varying age according to the species. But the adults
have the character, and tee forms which are without it are placed in
the genus Coptosoma, Desor. The alliance of CypTiosoma to the
Pseudodiadema-gTou.) is evident from the common external characters,
and there are points in the structure of the ambulacra which unite
the genera and at the same time refer to the Triplechinidse.
DiPLOPODiA VEESiPOEA, Phill., sp., uou Diplopodia subangularis,
McCoy.
This species, usually attributed to Pseudodiadema, is ver.- familiar
to the students of the fossils of the Coralline Oolite, and it has been
figured by Dr. Wright (op. cit. plate vii. fig. 4).
The nature of the construction of the ambulacra has not been
given, except in a general manner.
The diplopodous condition of the pairs of pores is well worthy
of study, and it can be examined in a specimen in mj possession.
Taking one of the zones of an ambulacrum, it is seen that the
first plate next to and in contact with the radial plate is a low and
narrow primary, with the adoral pore close to the median line of
the ambulacrum, and the aboral placed obliquely to it, the first-
mentioned pore being also on the line of suture between the first and
second plates (fig. 18). The second plate is at least twice the size of
Fig. 18 (see p. 452).
s2
the other, is slightly higher and much broader, and the adoral
pore reaches the suture between this and the third plate, being
placed almost directly actinally to the aboral pore of the first
plate. The aboral pore is far out of the vertical line of the corre-
sponding pore of the first plate. Both of the plates are primaries,
and do not form a compound plate. The third plate is high at the