96 SVEN LOVKN, ON THE ECHINOIUEA DESCRIBED BY LINN^US. 



characteristic tniit of leaving open laciinse, pits, grooves, »pun- 

 cta semipertusa'). At a greater distance aniong the Regu- 

 lares, it can be followed as a continuous expansion, the co- 

 louring element of the test, oftener compact, but not seldom 

 composed of exceedingly minute, brillant, nodules, as in the 

 Sphferechinus granularis or the Lytechiniis variegatus, or rising, 

 as in the Echinus escvilentiis and the E. miliaris, into wart- 

 like bosses. About all this, however, we are in the dark, being 

 i2:norant of the mode of development of the spines and pedi- 

 cellarife. And far away, among the Irregulares, structures are 

 met with that may be other modifications of the epistroma, 

 thns in Pygaster, in Echinoneus-), in the Clypeastridse, and 

 furthcr research will extend its occnrrence still wider. 



In recent Saleniae the berry-like protuberances have been 

 observed^); the sexual pores seem to open from under their 

 bases. In fossil forms the epistroma, generally luxuriant, co- 

 vers the expanded calyx with its raised sciitiform layer, rarely 

 smooth and even, oftener marked at the maroius of the ossi- 

 cles with deep lacuuae penetrating to the proper surface of 

 these, in some species mere points, >.puncta semipertusa», in 



others larg-e and roimdish holes, or 



*.". ••; o-rooves, clefts and fissures, but al- 



ways reducible to a typical model 



seen in certain species like the Sale- 



...; nia trigonata x\g. The dorso-central 



ossicle — as in the whole family — 



is to a great extent preserved intact 



in the adult, a minor portion only 



having been eroded for the periproct, 



The calyx of the Salenia tri- ^-j^g p-reater part of which has been 



gonata Ag. From Cotteäu. , r ^ 11 n r rm 



taken from the costals 1 and 5. ihe 



epistromal pentagon, heterotropous to, but concentric with, the 

 dorso-central ossicle, is readily recognised with the ridges it 

 emits into the radials. But from each of its live angles an- 

 other ridge, not present in the Arbacia because early löst, 



') See, on the stracture of the test in the Teumopleuridaj, its pits 

 and grooves, the researches of Professor DUNCAN in the Linnean Society's 

 Journal, Zoology, XVI, p. 343. 



= ) Compare Etudes s. I. Echinoidées, Pl. IX, fig. 79. 80. 



3) Etudes. Pl. XIX, fig. 159, 161, 163. — Al. ÅGASSiz, Blake Echi- 

 noidea, p. 20, pl. VI, fig. 17. 



