DESCRIPTIONS OF THE SPECIES. 183 



.1/. crenulatus. In the two former species there are three folds on each side of an 

 ambulacrum, and in the latter there are certainly two and perhaps three. 



The division of the spiracles by the deltoid ridge is much le.-s evident in some 

 species than in others. It is very complete in the .1/. angulatus and M. Sowerbii, 

 shown in PI. Tl. tigs. 7, 13 ; but less so in J/, crenulatus (PI. IV. fig. 1 ; PI. VI. fig. 8), 

 as the deltoid ridge does not extend, down on to the peristomial portion of the plate; 

 while it is almost entirely absent in two of the spiracles of M. elongatus seen in 

 PI. VIII. tig. 4. 



Species. To Mesoblastus we refer the following species : — 



Pentatrematites angulata, G. B. Sby. Carboniferous Limestone; Lancashire. 

 Pentatrematites crenulatus, Roemer. Carboniferous Limestone ; Tournay, 



Belgium. 

 Mitra elongata, Cumberland ( = Pentatrematites oblunga, G. B. Sby.). Car- 

 boniferous Limestone ; Lancashire. 

 Ihsoblastus giganteus, sp. nov. Carboniferous Limestone ; Lancashire. 

 Mesoblastus Pofei, nobis. Carboniferous Limestone ; Yorkshire and Lancashire. 

 Mesoblastus Soicerbii, nobis. Carboniferous Limestone ; Lancashire. 



We are strongly inclined to think that Granatocrinus glaber, M. & W., from the 

 St. Louis group of Illinois, should also be referred to this genus ; and the same is 

 probably true of some other American species hitherto described under Granatocrinus. 



Distribution. Mesoblastus is essentially a Carboniferous genus, and seems to occur 

 on both sides of the Atlantic, though more abundant in Europe, where it partially 

 replaces the American Pentremites. 



Type. Pentremites crenulatus, Roemer. 



Mesoblastus crenulatus, Boemer, sp. 



(PL IV. figs. 1, 2 ; PI. VI. figs. 8-10.) 



Pentatrematites crenulatus, Roemer, Archiv f. Naturgesch. 1831, Jakrg. xvii. Bd. i. p. 3G6, 



t. 7. f. 15 a-d. 

 Pentremitcs crenulatus, dc Koninck & Le Hon, Mem. Acad. Roy. Belgique, 183 1, tome xxviii. 



Mem. 3, p. 199, t. 7. f. 4 a-d. 

 Pentremites crenulatus, Dujardin & Hupe, Hist. Nat. Zooph. Echinod. 18G2, p. 96. 



Sp. Char. Calyx globular, or ovoid, attenuated more towards the summit than the 

 base ; summit convex, peristome depressed ; base truncate, slightly protuberant in 

 the middle, or indistinctly trilobate ; section pentagonal, with faintly concave sides ; 

 periphery at about one third the height from the base. Basal plates relatively large, 

 and slightly protuberant ; the pentagonal plate bears a median ridge, dividing the 

 surface into two planes ; the hexagonal ones each have two divergent ridges dividing 

 their surface into three planes ; around the articular facet each plate bears two (or 

 perhaps more) little nodes. Radial plates long and moderately broad, transversely 



