282 Messrs. P. H. Carpenter and R. Etheridge, Jun., 



singularly protean nature. We cannot even refer it to any 

 known family of Crinoidea, although in many respects it 

 approaches the Haplocrinidte very closely. 



The sources from which our material is derived are two. 

 The ample and fine collection of Dr. J. S. Hunter, of Braid- 

 wood by Carluke, has supplied us with two well-preserved 

 examples of the calyx. In the second place, we have been 

 permitted to use a very large series of specimens, showing 

 all stages of growth, from the collection of the Geological 

 Survey of Scotland. The examples in question were collected 

 and washed from shale by Mr. James Bennie ; and we are 

 indebted to the kindness of Prof. A. Geikie, LL.D., F.R.S., 

 for the loan of them. 



In the descriptions which follow we have united under the 

 one name a series of forms possessing up to a certain point in 

 tiieir organization the same general structure, but beyond this 

 differing in minor degrees, which we were at first sight in- 

 clined to look upon as probably of specific value. The finding 

 of a regular gradation, however, between the extreme forms of 

 the series lias led us to reconsider this view ; and we now 

 think the additional points of structure referred to may be 

 looked upon simply as an advance from a less to a more com- 

 plex condition in the same form. 



2. Descri])tion of the Genus and Species. 



Genus Allagecrtnus, Ether. & Carp. (gen. nov.). 



Gen. char. Calyx pyriform or cylindro- conical, composed 

 of five basals and five unequal radials, one to four of which, 

 or sometimes none, may be axillary. An oral pyramid of 

 five closely fitting valves, and of very variable height, is pre- 

 sent in the young, but is probably wanting in the adult. 

 Arms composed of elongated joints, sometimes forking twice. 

 Stem short and vermiform, of low rounded joints ; canal 

 circular ; terminal faces slightly granular. 



Ohs. Although the various individuals figured on Plates XV. 

 & XVI. differ from one another to a very considerable ex- 

 tent, both in size and form, we have been led to the con- 

 clusion that they are really all referable to one species and 

 represent various stages in its development. The most ad- 

 vanced, and probably fully grown, stage is shown in PI. XV. 

 figs. 1, 2, and 6. These are the only three tolerably complete 

 specimens of the adult that we have met with, and were all 

 found at the same locality. Fig. 2 represents that which is 

 most fully developed and also the best preserved of the three. 



