38 TEMNOPLEUEID/E. 
Arbaciadae. The next stage being the formation of low radiating spokes 
round the primaries formed by the running together of flattened miharies or 
secondaries. From this type of ornamentation the passage is an easy one 
to the marked and prominent ridges of Trigonocidaris, Dictyopleurus, and 
the like. But, as I liave shown when speaking of the changes due to growth 
in young Temnopleuridte, tlie presence of pits and sutures is a feature only 
developed with age, and the transition is insensible between the types in 
which the pits and sutures are formed by the modification of a flat surface 
due on one side to the thickening or elevation of nearlj' the whole plate, or, 
on the other, of only a portion of it. This still leaves, however, as charac- 
teristic of the Temnopleuridce and their nearest allies as limited by Duncan, 
the remarkable dowellina; of the sutural foces. 
The peculiar sunken pits of the Clypeastroids extending around the 
primary tubercles reach deep into the thickness of the test ; they are not 
to be regarded as merely sunken areolas. In some of the NucleolidaB we 
have a similar sunken area round the primaries ; on the actinal side, round 
the actinostome of such genera as Rhynchopygus, these pits are independent 
of the tuberculation, and form very deejjly sunken and irregularly shaped 
grooves in the thickness of the test. In Goniocidaris, another genus in 
which we have pits and sutural bands, they are not deep, and do not extend 
into the thickness of the test. 
Temnecliintis maculatus A. Ac. 
Lat. 26° 31' N., Long. 85° 53' W. Lesser Antilles, Florida. 73-229 fathoms. 
»^Q For list of Stations, see Bull. M. C. Z., V., No. 9, p. 189, 1878 ; VIIL, No. 2, p. 76, 1880. 
'7"1 ' ' This species has also been dredged by the U. S. Fish Commission off New- 
port in deep water. 
Trigonocidaris albida A. Ag. 
y^ Lat. 24° 15' N., Long. 82° 13' W. FloriJa, Lesser Antilles. 124-450 fathoms. 
^ For list of Stations, see Bull. M. C. Z., V., No. 9, p. 189, 1878; VIIL, No. 2, p. 77, 1880. 
J 
Echinus gracilis A. Ag. 
Straits of Florida, West Indies, East Coast of U. S., and as far north as off Martha's Vineyard, 
by the U. S. Fish Commis,sion. 93-200 fathoms. 
