184 CATALOGUE OF THE BLASTOIDEA. 



arched and vertically curved ; bodies small, concave in the middle line, bounded by 

 ridges proceeding obliquely from the radial lips ; limbs long, reaching to the summit, 

 truncated above, with convex radio-deltoid sutures ; sinuses very long, more or less 

 visible in a basal view, with subparallel margins and thickened edges, the surfaces 

 of the radial plates flattened or bevelled away immediately outside their edges ; lips 

 sharp and prominent, interradial sutures in slight concavities. Deltoid plates small, 

 elongately triangular, more or less horizontal, and with somewhat constricted apices, 

 which form a strongly crenulate (or punctate 1) border to the peristome. Ambu- 

 lacra projecting above the sides of the sinuses; lancet-plates exposed in the median 

 line for about two thirds of their length ; side plates oblong, thirty-five or more, 

 with large sockets bounded by V-shaped margins ; pores very small and inconspicuous. 

 Hydrospire-folds two (and perhaps three) on each side of an ambulacrum. The 

 four anterior spiracles more or less completely divided by a deltoid ridge of variable 

 width ; anal spiracle large, triangular-pyriform, with a reflected lip-like outer margin. 

 Mouth generally rather large. Basal plates and bodies of the radials with strong 

 equidistant granular ridges ; the surface of the radials carries fine close granular 

 lines crossing them obliquely from the sinuses in the direction of the interradial 

 sutures, whilst the bevelled bands are ornamented with strong subimbricating 

 chevron-like rugae; the deltoid plates are granular. 



Remarks. This species resembles M. Sowerbii (PI. VI. figs. 12, 14) in having a pro- 

 tuberant base, but in other respects its general form is rather more like that of 

 M. angulatus (PI. VIII. figs. 7, 8), which, however, is a larger species, and has a concave 

 base. The other European species of the genus are all much more elongate in outline 

 (PI. IV. fig. 3 ; PL VI. fig. 12 ; PI. VIII. fig. 1), and have larger deltoid plates than 

 M. crenulatus; while they also show no trace either of the subdivision of the base 

 into separate planes, or of the very marked crenulation on the central ends of the 

 deltoids, which are so characteristic of M. crenulatus (PL IV. fig. 1 ; PL VI. figs. 8, 9). 

 In weathered specimens this crenulation takes the form of a border of small pits 

 round the spiracles, as shown in PL VI. fig. 8. It is continued down the median 

 groove of the ambulacrum, as is well seen in PL VI. fig. 10, and also in Roemer's 

 figures 1 , which, according to Hambach 2 , "do not contradict" his statements as to 

 the preservation of a "zigzag plicated integument which covers the ambulacral 

 field." We do not think, however, that Hambach would have made these statements 

 if he had seen specimens of this type instead of figures only. The results produced by 

 the weathering of the ambulacra are well shown on PL IV. fig. 2. Fig. 1 represents 

 an individual in which the spiracles are scarcely divided, owing to the smallness of 

 the deltoid ridge. It is much larger in the original of PL VI. fig. 8, but does not 

 quite reach the apex of the plate, as in the British species (figs. 7, 13). 



Locality 'mil Horizon. Tournay, Belgium : Upper Carboniferous Shale, Carboni- 

 ferous Limestone. 



1 Archiv f. Naturgcsch. 1851, Jahrg. xvii. Bd. i. taf. iv. figs. 15 r, 15 d. 



2 Trans. St. Louis Acad. Sci. 1884, vol. iv. uo. 3, p. 539 



