200 Proepedirufs of the Royal Irish Acadevii/. 



somewhat in foiia, and to an extent that can hardly be ascrilied to the 

 different disposition of the animal when it was biuietl in the mud. At firet 

 sight the telson of specimen 4 (Plate XXV, figs. 2 and 2a) seems to differ 

 from that of the type almost sulliciently to wan-ant separation into another 

 species: but, as no other oljserved variation is as marked as ihis, this 

 procedure hardly seems justifie<l. 



VI. — Notes ox tok Specimkxs. 



In preparing the foregoing descriptions of the genus and type species, 

 attention has oidy been paid to such parts as are well pi-oserved and easily 

 • iljservable in the selected .specimens. When we come, however, to consider 

 the remainder of the available material, wliicli is inferior in point of preserva- 

 tion, we find ourselves on more doubtful ground. The visibility falls ofT in 

 some cases to such an extent that the mere changing of the power of the 

 microsco[>o or the direction of the illumination endows an organ with a 

 lafHinjjly difTorent a.spect. Under these circumstances it has .seemed 

 ina«Ivisable to lay any great stress on the differences between individual 

 ."ipecimens. 



Certain individuals do sIjow a distinct variation, which is perhaps most 

 marked in tlie case of the tebon. Thus the animal figured in Plate XXV 

 figs. 2 and 2a, has caudal furcae of unusual shape, lacking the curvature 

 characteristic of those of the type specimen. These straight furcae were 

 also apparent in specimen 13 (le.xt-fig. 5b), but in this case the preservation 

 was ver)' poor and the creature small and possibly immature. It should be 

 note<l also that in both the specimens with straight furcae the caudal spines 

 are less erect than in those with curved furcae. The shape of the mandible 

 was very elusive, .<o that, though wlien associated with these straiglit furcae, 

 it is marke<ily more sickle-sliaj>ed (Plate XXV, fig. 2 than in the more normal 

 specimens (Plate XXIV, fig. 1 ; Plate XXV, fig. 1, and text-fig 5a), in the 

 absence of more information and further specimens it seems more than rash 

 to claim a .sjiecific s , -^ for these variations. 



To facilitate futu: nee to llic original material, a list is appended of 



the existing specimens, with the number attached to them : — 



Specimen 1. — Limnestbcna anlra, <J : type ; figured Plate XXIV, fi^. 1, la, lb, Ic. 

 Deptli in bore, about asO feet. 



Specimen 2. — Good antennae and claw of one cla.sper, J ; figured Plate XXIV 

 figs. 2, 2«, 2b. Depth in bore, 833 feet. Good " Esllierian " shells, in 

 rbidin^ one large one (about 25 mm. long), not di.stingiii.shable from the 

 niotlcm Linina<iopsis, were found on this slab of rock. 



