16 SUPPLEMENT TO THE 



becomes developed ^Yitll age. It is plain, however, from the full-grown specimens 

 developed by Mr. Glass, that this does not take place in Centronella vir/^o. 



At p. 62 of the * Canadian Journal' for 1801 Prof. Billings described and figured his 

 Centronella as " having the general form of Terebratula. Dorsal valve with loop consisting^ 

 of two delicate ribbon-like lamellae, which extend to about half the length of the shell. 

 These lamellae first curve gently outwards, then approach to each other gradually, until 

 at their lower extremities they meet at an acute angle ; then, becoming united, they are 

 reflected backwards towards the beak in what appears to be a thin vertical plate. Near 

 their origin each bears upon the ventral side a triangular crural process." 



The type of Centronella given by Billings is C. glans-fagea. A preparation of the 

 loop in this species was made by Dr. Rominger in September, 1862, and figured by 

 Prof. Hall at p. 47 of the ' Sixteenth Annual Report of the Regents of the University of 

 the State of New York,' 1863. Dr. Rominger's preparation clearly show^ed that 

 Billings' description of the loop of C. glans-fagea was to some extent erroneous. ^Ir. 

 Glass says that in his first attempts to get at the loop of Centronella virgo he obtained 

 results similar to those figured by Prof. Billings, but afterwards found that his results were 

 incorrect through his having rubbed away a large part of the transverse band formed by 

 the front of the loop. By the rubbing away of this part the ridge or plate projecting 

 behind it showed as if it were, as described by Prof. Billings, a reflected plate proceeding 

 from the end of the loop. These remarks, however, do not apply to the profile figure 

 given by Billings, which does not resemble anything which Mr. Glass has seen whilst 

 making his preparations. Dr. Rominger's figure of C. glans-fagea, as given by Hall, 

 agrees with Prof. Billings' figure as to the crura, and almost entirely agrees with Mr. 

 Glass's preparations of C. virgo, as also with the preparations by Prof. Winchell of C. 

 Julia, with the exception, in the latter case, that Dr. Rominger figures the ridge 

 or plate on the ventral side of the loop as I have represented it and not as repre- 

 sented by Winchell, and that the crura are not shown in Winchell's figures. The 

 following is the careful description of Centronella Julia as published by Prof. Winchell : 

 — " A delicate ribbon-like loop originates from the stout blunt crura on each side of the 

 so5ket-valve, having its flat sides at first vertical. The two branches of the loop proceed 

 at first in lines parallel or a little convergent, and then gradually diverge, widening as 

 they proceed, and assuming an inclined position, until, approaching the front of the 

 valve by a regular curvature, the lower edge has become anterior, giving the band an 

 angle of 30^ with the plane of the shell. Approaching the median line the band rapidly 

 widens, the front margin is drawn forward in a long acumination, wdiile the inner margin 

 is regularly concave, except that near the median line it turns abruptly forward so as to 

 meet that line at an acute angle. The loop thus forms an urceolate figure on its inner 

 margin, and on the outer a somewhat oval one, truncated behind and attenuately acumi- 

 nate before. In the median line, where the two branches meet, both are suddenly 

 deflected downwards, forming a double vertical plate, not quite reaching the ventral valve. 



