126 Mr. T. TI. Withers on 



other specimens have been presented to the Geological 

 Department of the British Museum, registered In. 20588- 

 In. 20591. 



Holotype. The outer plate (fig. 1). 



Material. Thirteen pieces of shale ^vith several admedian 

 and outer ])hites. 



Desc7-iption. The plates {<re all much flattened and imper- 

 fect, and are preserved as mere films standing out white on 

 the rusty-brown shale ; they are of two kinds, the admedian 

 heart-shaped plates and the outer kite-sha[)ed plates. None 

 of the so-called "cancellated^^ plates have been noticed. 



Admedian plates roughly heart-shaped, broad, short, sub- 

 triangular, with the apex directed inwards, and a rather 

 Avide ill-defined fold extending from the apex to the 

 excavated portion of the proximal margin, the largest plate 

 having a height of 3'8mm. Proximal margin sinuous, the 

 middle portion deeply excavated ; inner (fixed) margin 

 rounded and markedly protuberant from tlie apex, much 

 more so than is the outer margin. The growth-lines are 

 very closely disposed, in some measure no doubt due to 

 crushing, and they are directed upwards on the margins, but 

 to a greater extent on the inner margin-. 



Outer plates kite-shaped, somewhat curved distally with 

 pointed apex, and a narrow submedian fold extending the 

 whole length of the plate and situated slightly nearer to the 

 outer margin, and there is a similar but narrower fold near 

 and parallel to the inner margin. The proximal margin is 

 slightly sinuous, being slightly excavated in the middle, the 

 outer proximal angle is broadlj^ and regularly rounded, and the 

 inner proximal angle narrowly rounded ; inner margin very 

 slightly concave, the proximal half almost straight ; outer 

 margin slightly convex. Growth-lines closely disposed, 

 6-7 to a millimetre, equidistant, crossing the median apico- 

 proximal fold at right angles, slightly concave on the inner 

 half of the plate and a little upturned at the inner margin, 

 and on the outer half they are broadly curved upwards, and 

 towards the outer margin are more crowded together. 



Remarks, and comparison with other species. The detached 

 plates of Plumulites are readily distinguished from the 

 probably homologous admedian and outer plates of Turri- 

 lepas. In Turrilepas the plates are much thicker, the 

 admedian plates have more laterally produced lobes and are 

 consequently more saddle-shaped, and the outer plates are 

 not acutely tapering at the apex, nor have they the median 



