DESCEIPTIONS OF THE BPECIE8. 301 



our materia] will permit us to form an opinion, A. tebragonua appears to be a con- 

 siderably larger and more robust species than A. Benniei, and this variation in habit 

 was probably accompanied by other structural differences. 



Locality and Horizon. Settle, Yorkshire; Carboniferous Limestone. 



Asteoceinus Benniei, Etheridge, Jim. 

 (PI. XIX. fig. 1 ; PL XX. figs. 3-20.) 



Astrocrinites Benniei, Etheridge, .Tun., Quart. Journ. Geol. Soc. 187G, vol. xxxii. p. 103, 



t. 12. f. 1-11, t. ]3. f. 12-22. 

 Astrocrinus Benniei, E. & C, Ann. & Mag. Nat. Hist. 1883, vol. xi. p. 237. 



Sj). Char. Calyx depressed-stellate, with deep reentering angles between the lobes; 

 anterior interradius occasionally much produced, though it may be shorter than 

 either of the lateral ones; summit flattened or a little concave; base flattened or 

 slightly convex. The azygos basal plate rounded triangular, the two others reaching 

 at most to the periphery. The two anterior radial plates are entire, regular, equal, 

 convex, narrowed below and expanding upwards, with their limbs reaching upwards 

 to the periphery ; the two postero-lateral radials agree with the anterior pair in 

 every particular except that the posterior limb in each, which is next to the azygos 

 lobe, is only partially developed ; the fifth radial is broadly triangular or rhombic, 

 convex, and a little pointed below. The four sinuses are short, extending for about 

 a third the length of the radials, with prominent lips ; the fifth sinus is only repre- 

 sented by an emargination of the upper edge of the azygos radial, and the lip is not 

 well defined. The anterior and two lateral deltoids are relatively large and strongly 

 cristiform, with constricted central ends. The four normal ambulacra are long, 

 slightly petaloid, and cross one another nearly at right angles ; lancet-plates narrow ; 

 side plates fifteen or more, inclined at a high angle ; the fifth or modified ambulacrum 

 more or less petaloid, with about five side plates on each side. One hydrospire-fold 

 on each side of an ambulacrum. The entire dorsal or lower surface of the calyx is 

 ornamented with closely-set, sharp, and tooth-like tubercles, with a plain smooth 

 apex and fluted sides, the tubercles becoming conical and obtuse on the radial limbs. 

 The crests of the deltoid plates have three or more rows of these tubercles, the central 

 row being the largest; some of them at least were punctate, and probably had spines 

 attached; the two elongated basals were marked with transverse scale-like ridges, 

 and the azygos radial plate which rests upon them has similar ridges arranged in a 

 vertical direction. 



Remarks. Since the description by one of us, ten years ago, of Astroeriiuis 

 Benniei, further examples of this remarkable type have come to hand, and the present 

 state of our knowledge of Blastoid morphology enables us to form a better idea of 

 its structure and systematic position than was possible in 187G. 



Some of the figures formerly given in illustration of this species exhibit features 



