DBSCBIFI [ONS OF THE SPECIES. 185 



Mesoblastus angulatus, G. B. Sowerby, sp. 

 (PI. VI. fig. 7; PI. \ III. figs. 7. s ; PI. XVII. fig. 9.) 

 Pentatrematites angulata, G. 1?. Shy., Zool. Journ. 1828, rol. iv. no. 13, p. s '.) ; ifiirf. 1834, 



vol. v. no. 20, pi. 33 Suppl., f. 1. 

 Pentremites angulatus, riiilli|is, Geol. York. pt. 2, 1836, p. .'-'07, t. 3. f. 13. 

 Orbtiremitesl angulatus, T. & T. Austin, Ann. & Mag. Nat. Hist. 1842, vol. x. p. 111. 

 Pentatrematites angulatus, Etoemer, Archiv 1'. Naturgesch. L85J, Jahrg. wii. lid. i. p. 'MY!. 

 Pentremites angulatus, Dujardin & Hupg, Hist. Nat. Zooph. Echinod. L862, p. 94. 

 Granatocrinus angulatus, E. & C, Ann. 6v Mag. Nat. Hist. 1882, vol. ix. p. 239. 



Sp. Char. Calyx angularly globose, inflated along the lines of the ambulacra; 

 summit more or less contracted ; peristome concave; base contracted, but generally 

 wider than the summit, concave, with a moderately deep columnar cavity, imme- 

 diately surrounded by the apices of the ambulacra ; section obtusely pentagonal, with 

 the sides flattened above, but. rather concave below ; periphery almost equatorial. 

 Basal plates small, limited to the columnar cavity. Radial plates large and exceed- 

 ingly long, reaching the entire length of the calyx, lateral margins converging below, 

 but rapidly expanding above, arched both laterally and longitudinally ; bodies very 

 small, confined to the columnar cavity, and inturned almost parallel to the vertical 

 axi- of the calyx ; limbs very long, reaching from just beyond the margin of the basal 

 cavity almost to the summit ; sinuses very long and narrow, parallel-sided, with 

 sharp edges ; lips small, but prominent, and scarcely visible in a side view, owing to 

 their inward flexure ; interradial sutures in slight concavities. Deltoid plates small, 

 elongately triangular, almost entirely confined to the summit, and hardly visible in a 

 side view, either horizontal or inclined inwards. Ambulacra projecting above the 

 margins of the radials. approaching one another closely at the base ; lancet-plates 

 narrow, hardly if at all exposed ; side plates small, placed at a very high angle, 

 forty or more ; pores small and numerous, excavated in the edges of the radials. 

 Hydrospire-folds three on each side of an ambulacrum ; tubes long; sacs pyriform. 

 Anterior spiracles almost horseshoe-shaped, within the area of the concave peristome, 

 opening obliquely upwards and inwards; anal spiracle oval-pyriform, with the outer 

 margin produced upwards and lip-like. Mouth small. Ornamentation minutely 

 lineate granular. 



Bernards. Mesoblastus angulatus may be readily distinguished by the inflated angular 

 form of the calyx, the long curved ambulacra, small deltoids, and the peculiarly 

 contracted summit and base. Seen in side view it somewhat resembles (iranatocrimis 

 orbicularis (PI. IX. figs. 11, 12), but in other respects the two types are very different. 



As in M. elongates (PI. VI. fig. 7; PL VIII. fig. 4), the deltoids are comparatively 

 very small, but the elongated shape of the calyx, both in this species and in M. Sowerbii 

 (PI. VI. fig. 12; PI. VIII. fig. 1), is quite unlike that of the present form. 



The double character of the spiracles is unusually distinct in this species (PI. VI. 

 fig. 7) ; for the deltoid ridge, though not so wide as in some forms of M. crenulatus 



2 b 



