194 MR. P. H. CARPENTER ON i^ ^LANOCRINTJS 



between the two measurements given above ; while the shape of 

 its muscle-plates is not constant, their upper ends being bluntly 

 pointed in some cases (like PL IX. fig. 1 a), but more squared in 

 others (like PI. IX. fig. 2 a). 



Diameter of the specimen figured (PI. IX. fig. 2), 13^ millims. 

 Total height 10^ millims. ; of the radials alone f>\ millims. 



All the Cambridge specimens ofAntedon costata agree with the 

 type in the first radials having a considerable outer dorsal sur- 

 face, so as to have been distinctly visible externally when the 

 second radials were in position. The same is the case with all 

 the adult specimens of A. costata figured by Quenstedt on pi. 96 

 of his ' Encriniden,' and also in nearly all the allied species figured 

 by de Loriol in his ' Fossil Crinoids of Switzerland.' In his 

 ' Jura,' however (pi. 88. fig. 10), Quenstedt gives a small figure, 

 which I reproduce here (PI. IX. fig. 4), of a form in which the 

 first radials have an unusually small exterior. The centrodorsal 

 and the other characters of the radials resemble those of the type 

 so far as can be judged from the figure, which is too small to be 

 quite satisfactory. The specimen is interesting from its being a 

 transitional form towards the next type, which must, I think, be 

 regarded as distinct from A. costata. 



II. — On pi. 51. fig. 36 of his ' Petrefactenkunde,' Quenstedt gives 

 a small and indistinct figure of a Nattheim specimen that differs 

 from the type species in the relations of the external surface of the 

 radials. It does not continue the upward slope of the centro- 

 dorsal as in the type, but is nearly at right angles to it, so as to 

 look almost directly downwards over the edge of the centrodorsal 

 beyond which it projects, and not downwards and outwards. 

 There is a small specimen in the British Museum from the same 

 locality that agrees with Quenstedt' s figure in this and other 

 features, but differs from it in points of detail. The articular 

 faces are much wider relatively to their height, and have a groove 

 along their dorsal edges just below the fossa for the elastic liga- 

 ment (PI. IX. fig. 3). There are large basals at the angles of 

 the calyx, and the centrodorsal is in the form of a truncated cone 

 bearing ten rows of cirrhus-sockets, but little traces of which are 

 visible, as the specimen is somewhat worn. The division between 

 the muscular and ligament fossae has also become obliterated, as in 

 most of the Nattheim specimens. 



The specimen figured is 6 millims. high, with a diameter of 

 8 millims. I propose the name Antedon truncata for this type. 



