F. Rutley — On CrystaUographic Formulce. 299 



implies that the shells are fossil Myas (I.e. p. 196, note). However 

 this may be, it is evident that a genus is required for the re- 

 ception of numerous Carboniferous shells vphich neither fall into 

 Sanguinolites on the one hand, or Edmondia on the other. Such 

 are those usually referred to Myacites, and so far as the 

 character of the present species can be made out, it appears to be 

 one of them. If Myacites and Allorisma are synonymous, it can 

 only be in the case of the latter genus, as afterwards restricted by 

 Prof. King (I.e., p. 196), because, as at first constituted (Annals and 

 Mag. Nat. Hist., 1845, vol. xiv. p. 316), Allorisma combined two 

 shells of totally different characters (Perm. Foss., p. 162). I propose 

 the name M. tenuilineata for this form, which was kindly lent me 

 for description by Mr. D. J. Brown, of Edinburgh (by whom it was 

 found). Although not in the best state of preservation, its specific 

 characters appear to be these : 



Myacites? [Allorisma) tenuilineata, sp.nov. — Transversely elongate, 

 produced posteriorly, inequilateral ; anterior side short, rounded ; 

 posterior side narrowed, acuminated, somewhat produced ; ventral 

 margin convex; dorsal margin gradually descending to a blunt 

 termination ; beaks large, depressed, apparently somewhat incurved ; 

 shell convex, most so a short distance below the beaks, whence the 

 sides slope rapidly to the ventral margin; surface with numerous 

 close, thin, concentric lines, which here and there show traces of 

 granulation. 



Locality. — Lower Limestone series of Midlothian, at Cousland, 

 near Edinburgh. The surface of the shell is much worn, but with 

 a good lens traces of the granulation can be detected. This would 

 still further tend to ally it with Myacites. 



V. — On a New Method of Wkiting CRXSTAiiLO graphic Formula. ^ 

 By Fkank Rutley, F.G.S., Geological Survey of England and Wales. 



CETSTALLOGEAPHIC, like all other formulae, are simply 

 short-hand methods of describing that which could otherwise 

 only be rendered intelligible by the expenditure of many words, 

 and, in type, by considerable waste of space. Anything, therefore, 

 which tends to simplify and contract formulge, without diminishing 

 the amount of information which they convey, must necessarily be 

 advantageous. The different systems of notation used at the present 

 time by eminent crystallographers render the comprehension of 

 their formulse somewhat difficult to the student; and it would doubt- 

 less be productive of much satisfaction if a universal system of 

 CrystaUographic notation could be adopted. 



The method which I am about to describe will, I think, be found 

 to fulfil all ordinary requirements, and might, if adopted, save time 

 and space, and likewise diminish some of the difficulty experienced 

 by the student. The symbols which I propose to use present, so far 

 as I can see, no obstacle to the accurate rendering of any formula, 



^ The system of notation adopted by Prof. Dana is certainly as brief as the one 

 now proposed, but does not appear to me to be so explicit. 



