20 T. MeUard Reade — On Miniature Sand-domes. 



hinge of the ventral valve that foi'med the denticles. These work- 

 ing- mechanically in the softer calcite of the dorsal valve, through 

 the continuous opening and shutting of the valves, would naturally 

 wear out a row of pits corresponding with the number of denticles. 



The object which these denticles and their sockets had to serve in 

 the economy of this organism was probably that which Dr. Davidson 

 has suggested to me by letter, viz. " to steady the valves, especially 

 when the hinge-line was long and the teeth not very large." I 

 have also to note that in several specimens that I have examined 

 there is clear evidence of successive layei's of shell-growth along the 

 area of the hinge-line of the ventral valve. These stages show in 

 the rounded appearance of the calcite layers around the denticles 

 that there had been in the growth of the hinge-area periods in which 

 for a time it had remained stationary, and it has also occurred to me 

 that the bifurcation seen in some of the lines that went to form the 

 denticles may be satisfactorily explained on the supposition that 

 there had been at these points of the hinge-area originally two lines 

 of aragonite, forming two separate denticles, which from some 

 cause afterwards converged so as to form only one denticle. 



The Scottish specimens of Carboniferous Spirifera in which I have 

 found the clearest evidence of the denticulated hinge-line are those 

 obtained from shales in which the shells and other organisms have 

 not been much mineralized. Those from the harder limestones, 

 although showing in many specimens the vertical lines on the 

 hinge-area distinctly, yet their valves are so firmly locked together 

 that evidence of the denticles can only be obtained by carefully 

 scraping the edge of the hinge-line with a knife, and etching the 

 area with acid. 



The species upon which I have worked is S. trigonalis, Martin, 

 and its variety S. hisulcata, Phillips, which is similarly denticulated. 

 On the thin-shelled and short-hinged species, such as S. glabra, 

 Mart., and S. lineata, Mart., denticles seem to be absent, or, if present, 

 are only very feebly developed. An examination of other straight- 

 hinged genera of Brachiopods, such as Streptorhynchus and StropJio- 

 mena, from our Scottish Carboniferous strata, show only in some 

 Instances traces of vertical lines on the hinge-area and very feeble 

 indications of denticles, but this may be due to the less perfect 

 preservation in the beds where they have been found ; for in the 

 Strophodonta from the Silurian strata of America the denticulated 

 hinge-line is often beautifully preserved. 



VI. — Miniature Domes in Sand. 

 By T. Mellaed Eeade, F.G.S. 



IN walking along a stretch of very fine smooth sandy shore at 

 Blundellsands, I was very much struck at finding a portion of 

 it studded over with numerous bosses of sand from ^ in. to 3 inches 

 in diameter. Wondering what could be the cause of this singular 

 phenomenon, I dissected some of them with my knife, and found in 

 all cases a cavity below corresponding in extent and height to the 



