BY R. ETHERIDGE, JUNR. 755 



versely arranged ornament is broken up into a festoon-like 

 appearance by delicate longitudinal, inequidistant grooves. The 

 former is directed convexly upwards towards the aperture on the 

 chief face of the shell, sigmoidally curved on the sides and 

 horizontal on the lesser of the principal faces. 



The most interesting point, however, is the operculum. This 

 organ in HyoUthes consists of two essential parts, — a chief semi- 

 conical portion, the semicircular base of which is applied to the 

 margin of the larger face ; and a smaller portion separated from 

 the former by two rather deep grooves radiating from an umbo, 

 and always inclined more or less at an angle to the major portion. 

 The operculum of H. lanceolatus, of which we possess an excellent 

 example separated from the shell, and another attached in situ, 

 is ornamented in a similar manner to the shell, but the festoon 

 shaped striae become concentric in the strict sense of the word, 

 and are uninterrupted by regular radiating grooves, although 

 from the umbo to the convex margin of the larger half proceed 

 two or three indefinite radiating wrinkles. On the surface of the 

 smaller concave portion of the operculum are two additional 

 diverging grooves from the umbo, separating off, with the 

 assistance of those formerly mentioned, two elongately triangular 

 spaces. The concentric lines on the smaller portion are much 

 coarser than on the conical or convex half. On the whole this 

 operculum has much the appearance of some Chiton plates. 



The specimens are taken to be HyoUthes lanceolatus, although 

 the transverse section of the shell is not so trigonal as that repre- 

 sented in Morris's figure ; neither have I seen any trace on the 

 internal cast of the obtuse ridges described by that author. The 

 largest measures nearly one and a-half inches in length, somewhat 

 less than the type, and the operculum is five-sixteenths of an inch 

 in its longest diameter. 



The present examples were obtained by Mr. Waterhouse at the 

 new shaft of the Maitland Coal Company, between the West 

 Maitland and Farley Railway Stations on the Northern line ; 

 and at Silkstone, near Tumbleby, in very hard but similar 

 nodules to the ConularicB, and from a like horizon. 



