on a neiv Fossil Ciiripede. 323 



Mr. Darwin's nomenclature of the valves. The si)ecinien is still 

 too inii)ertect to detennine the structure of the genus with accu- 

 racy, though I rather think that, on the whole, the additional 

 portions preserved add to tlie probability of the general correct- 

 ness of Mr. Darwin's restoration. Another view of the struc- 

 ture a|)pears, however, to be possible, and this view I shall ex- 

 plain after having described the specimen in full. 



The capitulum consists of live valves, evidently the valves of 

 one side ; a small fragment of one scaled off, showing the inner 

 aspect of the corresponding valve in immediate apposition. Fol- 

 lowing Mr. Uarwin, the right-hand valve in the figure is the 

 scutum, rather broadly triangular, the base with a convex outline ; 

 an obscure ridge traverses tiie plate longitudinally near the 

 oeclndent margin, and towards this ridge the nearly transverse 

 lines of growth slightly dip on cither side. Beyond the occlu- 

 dent margin a small portion of the convex interior of the op- 

 posing scutum has been exposed. Both of the scuta are some- 

 what displaced downwards, and the opposite peduncular plates 

 are broken. 



The scutal latus is broadly triangular; its slightly convex 

 scutal margin overlaps the edge of the scutum, and its almost 

 perpendicular tergal margin overlaps the tergum. A ridge 

 passes from the apex to a projecting angle on the base, about 

 one-third of the breadth of the valve from the scutal margin ; 

 the lines of growth are nearly transverse, following the contour 

 of the base of the valve, inclining slightly from either side to- 

 wards the ridge. The second latus is a little narrower, the tergal 

 margin concave, overla])ping the tergum ; the outline of the 

 carinal margin slightly convex ; the base straight, exactly cor- 

 responding to the second plate of the upper transverse row of 

 the peduncle ; growth downwards. The next plate is closely 

 applied to the left margin of the second latus ; it is narrow, 

 triangular, almost linear, resting by a narrow, slightly convex 

 base upon the upper plate of the narrow carinal row of peduncular 

 plates, to which it exactly corresponds in breadth, and with 

 whose straight edges its left contour is continuous. This valve 

 is equal in height to the second latus ; the lines of growth are 

 transverse, the development having taken place entirely down- 

 wards ; both lateral margins are well defined, and beyond the 

 left margin the edge of another plate has been exposed, exactly 

 corresponding to it. 



Adopting Darwin's idea, this valve must be either one of the 

 valves of a split carina — one of the parictcs of a carina in which 

 the tectum is undeveloped ; or we must suppose the carina to 

 have been composed of two parietes and a separate tectum, and 

 the tectiim to have been lost. 



21* 



