38 TEMNOPLEUEID^E. 



Arbaciadse. The next stage being the formation of low radiating spokes 

 round the primaries formed by the running together of flattened miliaries or 

 secondaries. From this type of ornamentation the passage is an easy one 

 to the marked and prominent ridges of Trigonocidaris, Dict3"opleurus, and 

 the like. But, as I have shown when speaking of the changes clue to growth 

 in young Temnopleuridse, the 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 nearly the whole plate, or, 

 on the other, of only a portion of it. This still leaves, however, as charac- 

 teristic of the Temnopleuridie and their nearest allies as limited by Duncan, 

 the remarkable dowelling of the sutural faces. 



The peculiar sunken pits of the Clypeastroids extending around the 

 primary tubercles reach deep into the thickness of the test ; the}' are not 

 to be regarded as merely sunken areolas. In some of the Xucleolidae 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 tuberculatum, and form very deeply sunken and irregularly shaped 

 grooves in the thickness of the test. In Gonioeidaris, another genus in 

 which we have pits and sutural bands, they are not deep, and do not extend 

 into the thickness of the test. 



Temnechinus maculatus A. Ac. 



Lat. 2G° 31' X., Long. 85° :.:;' W. Lesser Antilles, Florida. 73-ii9 fathoms. 



For list of Stations, see Cull. M. ( '. /., V.. No. 9, p 189, L878 ; VIII., No. -2, p. 76, 1880. 



This species has also been dredged by the U. S. Fish Commission off New- 

 port in deep water. 



Trigonocidaris albida A. Ao. 



Lat. 24° 15' N., Long. 82° 13' W. Florida, Lesser Antilles. 121-150 fathoms. 



For li.st of Stations, see Hull. M. 0. Z.. V., Xo. 9, p. 189, 1878; VIII., Xo. 2, p. 77, 1880. 



Echinus gracilis A. Ag. 



Straitsof Florida, W't [ndii . East Coa i of U.S., and as far north as off Martha's Vineyard, 

 by the U. S. Fish Commission. 93-200 fathoms. 



