202 CATALOGUE OF THE BLASTOIDEA. 



tip. Char. Basal plates forming a large and long cup, subangular or angularly 

 rounded in section ; the sides at the upper end are more or less flattened, whilst 

 below they are grooved along the lines of suture, and the bodies of the plates are 

 more sharply angular. The upper ends of the two large plates have median re- 

 entering angles, whilst the third or small basal is pointed above ; the lower end of 

 the cup is triangular, and the columnar facet small and round. When separated the 

 plates are found to have a considerable thickness, the lower part of the cup becoming- 

 solid, except for the continuation of the columnar canal. 



Remarks. We have already called attention to the probable Blastoid nature of 

 this peculiar fossil 1 , and now, through the kindness of M. Munier-Chalmas, have had 

 an opportunity of examining some examples of it, one of which (natural size) is shown 

 on PI. V. fig. 22. 



There can, we think, be little doubt that it is the base of what must have been a 

 large species of Metablastus. The lower part of it is distinctly trihedral, and the 

 upper part roundly pentagonal, the one condition passing into the other in the 

 manner described on pp. 16-18. All the ridges which are characteristic of the basal 

 plates of a Blastoid can be distinctly traced upon the specimen which we have figured 

 (PI. V. fig. 22). The large plate which is seen in the figure is the basal, y 2 , and its 

 median ridge is No. 4, the one corresponding to radius C ; while the grooves at its 

 sides mark the lines of the interbasal sutures. 



This remarkable fossil was discovered by M. Munier-Chalmas, and was described 

 by him under the name of Belemnocrinus Cottaldi in the following terms 3 : — " Le 

 calice, qui est conique, se compose de 5 pieces longitudinales. II presente, vers sa 

 base, 3 sillons externes, et, a sa partie superieure, une cavite pentagonale tres pro- 

 fonde." As, however, it was subsequently discovered that the name Belemnocrinus 

 had been preoccupied by White, it was changed into Belocrinus in 1881 4 . We 

 pointed out in 1883 5 that the fossil appeared to us to be nothing but the elongated 

 basal cup of a Troostocrinus or Pentremitidea ; and, after examining specimens of it 

 for ourselves, we decided to refer it to Troostocrinus. But when it became necessary 

 to limit the meaning of this name in the sense explained above, and to refer Belo- 

 crinus Cottaldi, together with most of the species of Troostocrinus, to a new genus, 

 we did not feel ourselves called upon to adopt M. Munier-Chalmas' generic name. 

 For we have no knowledge of the summit characters of the species, and his descrip- 

 tion of it as having fixe basals is certainly incorrect. We should say, however, that 



1 Ann. & Ma-. Nat. Hist. 1883, vol. ix. p. 245. 



- See tin' diagrams on pp. 13, 17. 



:t Journ. Conchyl. 187'i, torn. xvi. p. In 



4 Boll. Sue. Geol. do France, 1881, tome ix. p. 503. 



• Ann. & Mag. Nat. Hist. 1883, vol. xi. p. 245. 



