DESCRIPTIONS 01 THE SPECIES. 189 



resting naturally on their apices; summit more or less acuminate ; greatest periphery 

 nearly equatorial ; section pentagonal, the sides above the equator almost flat, but 

 below it rapidly becoming concave in the line of the interradial sutures; base 

 concave and much contracted. Basal plates within the central depression, and com- 

 pletely concealed from sight in a side view of the calyx. Radial plates verj long, 

 much arched both longitudinally and transversely ; bodies very small ; limbs very 

 long; radial sinuses narrow, decreasing in width but slowly, their margins thickened, 

 with a narrow and rather concave band on the surface of the limbs, following their 

 whole course. Deltoid plates very small (ill-preserved in all specimens examined). 

 Ambulacra much arched, projecting above the margins of the sinuses; lancet-plate 

 narrow and steep-sided, but with the median groove exposed ; hydrospire-plate wide ; 

 pores exceedingly numerous, small, round, and close together. Hydrospire-folds two 

 on each side of an ambulacrum. Spiracles small and close to the central aperture. 

 Ornament consisting of longitudinal and transverse rows of striae which give rise to a 

 minute reticulation. 



Remarks. The collection made by the late Mr. John Ilofe, F.G.S., contained a 

 mutilated specimen, which we formerly believed to be an Acentrotremites ; but the 

 temporary acquisition of additional material from the collection of Owens College, 

 Manchester, through the courtesy of Prof. W. Boyd Dawkins, F.R.S., has convinced 

 us that it should rather be referred to Mesoblastus. None of the specimens exhibit 

 the summit in a good state of preservation, although there is quite sufficient evidence 

 to show that the spiracles are formed after the type of Mesoblastus rather than that 

 of Accntrotremites or of Granatocriuns. 



The base of 21. Rqfei is concave, as in 21. elongatus and 21. angulatus (PI. VIII. 

 figs. 3, 8), and it is thus easily distinguished from 21. crenulatus and 21. Sowerbii 

 (PI. VI. figs. 9, 12, 14), in which the base is protuberant. 21. Rofei is distinguished 

 from 21. elongatus (PI. VIII. fig. 1) by the greater robustness of the calyx, flatter 

 sides towards the summit, and about the equator, narrower ambulacra, and in all 

 probability by possessing much smaller deltoid plates. As regards 21. angulatus, the 

 basal cavity is smaller than in the present species, the sectional diameter of the calyx 

 much greater, and the form generally broader and shorter (PI. VIII. figs. 7, S). A 

 partially decorticated specimen of M. Rofei exhibits two hydrospire-tolds on each side 

 of an ambulacrum, but we are not in a position to state whether this was the normal 

 number or not. The external ornament closely resembles that of Granatocrinus 

 elUpticus (PI. VI. fig. 21 ; PL VIII. figs. 1G, 19). 



We have much pleasure in associating with this interesting species the name of 

 the late Mr. J. Rofe, who was one of the first to realize the true morphological 

 nature of many portions of the Blastoicl economy. 



The geological collection of Owens College, Manchester, contains another species 

 of Mesoblastus, kinoly lent to us by Prof. Boyd Dawkins, F.R.S., which we purpose 

 shortly to describe elsewhere under the name of 21. giganteus, from its relative size 



