ECHINUS. 3 



essentially, in a minute character, which is constant in all the numerous examples sub- 

 mitted to my examination ; viz., in the presence of a minute granule separating the pores 

 of each pair. Otherwise, it differs in presenting more prominent bosses upon which the 

 spiniferous tubercles are placed, and in the more irregular dimensions of these organs. 

 The base has constantly a tendency to concavity, not seen in Echinus sph(Bra. At the 

 same time, I believe it to be a variety of another and rarer British species ; one com- 

 municated to me from the Coast of Cornwall by my friend Mr. Peach, and described at 

 the British Association at Edinburgh, in 1850, as a form of Echinus melo of Lamarck. 

 It would appear, however, that under the name of E. melo, Lamarck confounded two very 

 distinct species, and that the true E. melo is that enumerated under the same name by 

 Agassiz and Desor, a Mediterranean species, which (after an examination of the original 

 examples in the collection of the Jardin des Plantes,) does not seem to me to differ 

 essentially from the Ecldmis Flemivgii of the British and Norwegian Seas. It results that 

 a new name must be given to the species before us, whether it be considered strictly 

 identical with the Cornish (and Mediterranean also) sea-urchin alluded to before, or be 

 regarded as an extinct form, as yet peculiar to the epoch of the Coralline Crag. 



Body varying in convexity, a slightly depressed spheroid swelling out below ; in some 

 specimens obscurely pentangular, divided into five broad (or interambulacral) and five 

 narrow or ambulacral segments, separated from each other by avenues of pores, which are 

 arranged in oblique rows of three pair in each row. Towards the middle of the sides, the 

 breadth of an interambulacral segment, as compared with an ambulacral, is as 5 to 2. All 

 the plates are thickly covered by tubercles, of which the primaries are slightly unequal in 

 size. The tubercles ai"e round, imperforate, and placed on the summits of broad, gradually 

 swelling bosses. The interambulacral plates are very broad in proportion to their height. 

 The broadest of them bear about nine primary tubercles, which are arranged in one single 

 and one half row, the latter towards the truncated or ambulacral end of each plate. 

 There are about two large primaries on each ambulacral plate, the smaller ones innermost. 

 Towards the superior extremities of the ambulacral avenues one row only becomes promi- 

 nent. Among the primary tubercles are a few secondaries and many miliary granules. 

 Between the two pores of a pair, there is usually a miliary granule. The oral aperture is 

 one third broader than the apical disk, and occupies about one third of the breadth of the 

 entire test. It is placed in a slight concavity, and its margin is gently indented by 

 notches, with rctlexed margins at the interambulacral sides of the avenues. The apical 

 disk is not preserved in any of the specimens which I have examined. Internally, the 

 pores of the avenue appear widely disjoined, and those next the ambulacral segments are 

 larger than the opposite ones. 



The spines are stout, but not very short. They are finely grooved, with numerous 

 narrow sulci, the interspaces being smooth, and slightly convex. 



A good example measured two inches and two tenths in height by three inches in 

 breadth. 



