286 TEMNECHINUS MACULATUS. 



Temnechinus maculatus 



IGenocidaris maculatus A. Agass. 1869. Bull. M. C. Z. 

 ! Temnechinus maculatus A. Agass. 1S72. Rev. Ech., Pt. I. 



/'/. VIII. f. 1-18. 



Saving examined lately several species of Temnechini from the London 

 Crag, contained in a fine collection of fossils from the Crag, sent to the 

 Museum by Dr. Q nimby of Liverpool, I am inclined to regard this as a living 

 species of Temnechinus, although it presents, even in the largest specimens 

 received, very marked differences from those of Temnechinus figured by 

 Forbes in his British Tertiaries. 



This small Sea-urchin was described in the Preliminary Report as Geno- 

 cidaris maculata ( /'/. VIII. f. l). It is closely allied to Opechinus, which 

 Desor separated from Tcinnopleurus. The spines ( PI. VIII. f. 5) resemble in 

 their structure those of Temnopleurus, but are shorter; the Sea-urchin with 

 its spines resembling a Psammechinus, and basing, like it. a large number 

 of secondary tubercles, of nearly uniform size, closely crowded together (PL 

 VIII. f. 4), but of a peculiar chiselled structure round the base of the pri- 

 maries (so that it may be said that this genus is a Psammechinus among Tem- 

 nopleuridae), there is a principal row of tubercles in the ambulacra] and 

 interambulacral area larger than the others. The poriferous zone is narrow; 

 the pores, separated by an arched ridge, are arranged in an unbroken, slightly 

 undulating, vertical row. The primary tubercles are smooth, imperforate. 

 Near the base of the tubercle in the interambulacral spaces the test is orna- 

 mented by pits specially marked near the suture of the plates; in small speci- 

 mens (PL VIII. f. 11), the small tubercles are frequently connected by a 

 ridge with the main tubercles, and in still younger specimens (PL VIII. f. 

 H), before the secondary tubercles are well separated from the ridges, they 

 form spokes radiating from a hub, similar to the structure of the tubercles in 

 Glyphocyphus radiatus, and some species of Echinocyphus. The genera 

 Opechinus, Microcyphus, Trigonocidaris, and Temnechinus form a transition 

 between Echinus (Psammechinus) and Temnopleurus. The actinal membrane 

 is bare, with the exception of the ten small circular buccal plates. The acti- 

 nal opening is not large, with slight indentations ( PI. VIII. f. ..') ; in smaller 

 specimens the actinal system is nearly circular (PL VIII. f. 15), the test is 

 irregularly covered with pedicellariae, having a blunt bead surmounting a 

 long, slender stem, articulating upon a shorter, stout rod (PL VIII. f. 6). 

 The abactinal system is peculiar, as we find in the largest specimens even 



