TEMNOPLEURID.^. 37 
TEMNOPLEURIDiE. 
Duncan * has, in interesting articles on the pits and sutures of Temno- 
pleurus and on the structure of Pleurechinus, called attention to the im- 
portant differences existing between the Temnopleurida3 of the type of 
Temnopleurus proper and its allies, and such genera as Temnechinus and 
Trigonocidaris, which have been associated with them. 
He proposes to place on one side the genera' Pleurechinus, Temnopleurus, 
Salmacis, and Amblypneustes, which have true pits, and on the other side 
the genera Temnechinus, Trigonocidaris, Paradoxechinus, and Glyphocy- 
phus, which have raised ribs. 
The structural difference so well pointed out by Duncan is an important 
one ; he says he was unable to find, in the specimens of Temnechinus from 
the Crag which he examined, any trace of the remarkable " deep inward 
undermining or penetrations of the test " of Temnopleurus. The specimens 
of Temnechinus macitlatus of different sizes which I have examined show 
no trace of pits, nor of this system of dowelling at the junction of the 
plates. I have also again examined specimens of the recent Trigonocidaris 
albida, and do not find in that species either the sunken pits of Temno- 
pleurus proper or the dowelling. 
Duncan and Sladen t have figured in the fossils of Western Sind two other 
genera closely allied to Trigonocidaris : Dictyopleuriis and Arachnopleurus, 
in which the grooved and pitted ornamentation of the test is produced 
entirely by ribs and elevations. The peculiar structure of the ornamentation 
of the genus Progonechinus shows how difficult it may become to maintain 
the distinction suggested by Duncan. 
I had already called attention in the Revision of the Echini, p. 286, to 
the character of the ornamentation of the test of some of the Temnopleurida?, 
and to its probable derivation from a more simple type of ribbed ornamen- 
tation, such as is formed by the radiating arrangement of miliaries and 
secondaries round the primary tubercle of some of the Triplechinidae and 
* P. M. Duncan, On some Points in the Morphology of the Test of TemnopIeuriJae, Journal Linn. 
Soc. London, 1882, Vol. XVI. p. .343. On the Genus Pleurechinus, L. Agassiz, Journal Linn. Soc. 
London, 1882, Vol. XVI. p. 447. 
t Mem. Geol. Survey of India, Ser. XIV., Vol. I., The Fossil Echinoidea, Fascicul. IL Cal- 
cutta, 1882. 
