254 CATALOGUE OF THE BLASTOIDEA. 



small, concave, with a central depression ; limbs broad, obliquely truncated above ; 

 sinuses very long, almost reaching to the basi-radial sutures ; sides parallel, and with 

 sharp edges; lips acute; radio-deltoid sutures either equatorial or slightly nearer the 

 summit, broadly V-shaped, and each half either straight or gracefully curved upwards. 

 Deltoid plates elongately and unequally rhombic, acutely pointed and constricted at 

 their inner ends, sometimes with a faint and granular median ridge ; their apices 

 acutely pointed, constricted, and thickened so as to form nodes. Ambulacra narrow, 

 not projecting above the edges of the sinuses ; lancet-plate exposed in the median 

 line almost throughout its entire length ; side plates forty-five and probably more, 

 their inner ends projecting above the edges of the food-groove ; pores very numerous, 

 excavated out of the side plates. One hydrospire-tube on each side of an ambula- 

 crum ; its sac large and round, or oval in section. Spiracles perforating the enlarged 

 apices of the deltoids, and opening obliquely inwards and upwards. Ornament on 

 the radials and deltoids consists of a fine granulation arranged in lines parallel to 

 the margins of the plates. 



Remarks. This is certainly the most abundant of all the British Blastoids, G. I)er- 

 biensis being the only one which approaches it in this respect. The Rofe collection 

 contains several fragments of Carboniferous Limestone from Lancashire which are 

 full of broken calyces of this species, many of which are of the utmost value from the 

 way in which they illustrate certain points of structure (PL VIII. fig. 20 ; PL X. 

 figs. 12-15) ; but we have been quite unable to obtain any information as to the 

 particular horizon or locality at which they were found. 



G. ellipticus is readily distinguished from G. Derbiensis by the smaller size of its 

 deltoid plates, but it resembles that species (PL IX. figs. 3, 4), and also G. orbicularis 

 (PL IX. fig. 13), in the approximation of the ambulacra to the basiradial sutures, 

 though it is closer in this species than in any other. Furthermore the concave and 

 narrow base is altogether different from the broad flat base of G. campanulatiis and 

 of G. McCoyi (PI. VIII. fig. 13 ; PL X. fig. 6). The nearest ally of G. ellipticus, in 

 the characters of the summit as well as in those of the base, is unquestionably 

 G. orbicularis (PL VIII. figs. 17, 18; PL IX. figs. 13-15). But it is readily distin- 

 guished by its more globular calyx and larger size, and also by the different characters 

 of its ambulacra. The proximal edges of its outer side plates are cut away to form 

 the hydrospire-pores (PL IX. fig. 10), the distal edges of the side plates being quite 

 straight while the grooves which end in the sockets that they bear start from the 

 distal edges of the outer side plates. On the other hand, in G. ellipticus the pores 

 are excavated out of the side plates themselves (PI. VIII. fig. 21), the upper edges of 

 the outer side plates being quite straight, and not at all emarginate. The grooves 

 communicating with the sockets on the side plates arise from the sutures separating 

 the side plates themselves, and must have been in direct communication with the 

 pores. The granular ornament of the calyx in well-preserved specimens is very coarse 



