18 Mr. John Young — On the Hinge of Sjnrifer. 



stomata. This position is diametrically opposed to the dictum of 

 A. Agassiz, that the Galeritidge have no affinity with Echinoneus 

 (" Revision," p. 332) ; but it assists him in his comparisons of 

 Cystechinus with ancient forms. Loven, whilst tacitly acknowledg- 

 ing the old notions about Galerites, showed there are affinities 

 between the Echinoconidge and Echinonidee. 



Y. — On the Denticulated Structure of the Hinge-line of 



Spiiufera trigonalis, Martin. 



By John Young, F.G.S., 



of the Hunterian Museum in the University of Glasgow. 



RECENTLY, when examining some weathered fossiliferous lime- 

 stone shale from the Lower Carboniferous strata of East 

 Kilbride, Lanarkshire, ray attention was attracted to some fragments 

 of the valves of Spirifera trigonalis, Martin, in which I noticed, on 

 the hinge-line of the dorsal valve, a row of small, round, hollow 

 pits, and on the hinge-line of the ventral valve, a corresponding row 

 of small, projecting, rounded denticles. These characters I had not 

 noticed before, and on searching further, I found other fragments of 

 the valves showing the same thing. This led to an examination 

 of more perfect specimens of this Spirifera, contained in my own 

 collection, and that of Dr. J. R. S. Hunter, of Braidwood, Carluke, 

 and in one example, where the valves had slightly opened through 

 pressure, on clearing away the shale, I found, on the outer edge of the 

 ventral valve, a distinct row of small projecting denticles, that had 

 evidently fitted into hollow pits or sockets in the dorsal valve, but 

 from the way the valves had shifted in this specimen these were not 

 seen. These denticles, when looked at externally, are nearly as 

 numerous, and much of the same size, as those seen in many of the 

 hinge-lines of shells of the genus Area, only in this genus the teeth 

 are the same in each valve, and lock into each other. 

 Spirifera trigonalis, Martin. 



Diagram sketch, nat. size, valves slightly open to show 

 the denticulated hinge-line and pits. 



The denticles, as already stated, project from the outer edge of 

 the hinge-line of the ventral valve, which is seen to be bevelled from 

 within outwards so as to present a moderately sharp edge, and on 

 this edge the denticles are situated. On a specimen, measuring one 

 inch and three-quarters in length along the hinge-area, thirty-five of 

 these small denticles may be counted on either side of the central 

 triangular fissure. Sometimes there are more or less, their numbers 

 generally corresponding in most specimens with the extent of the 

 hinge-area. 



