188 RECORDS OF THE AUSTHALTAX MUSEUM. 



length in i^elation to the width is so much more dispi-oportionate than in 

 M. viorri'i^ii proper. Some little distortion has taken place, bat even 

 allowing for this the cinctures, strong keel-like diagonals, and nearly flat 

 posterior slopes, are self evident. The concentric lines of decoration are 

 remarkably fine and even, and quite unlike those of the M. earinala group, 

 at Fai'ley ar6 again internal casts, which also allowing for some distortion 

 are very similar to this Lochiuvar specimen. 



For the present I prefer to regard this shell simply as a variety of 

 M. morrisii, but the long, almost " snout-like " posterior end, lends so 

 marked an appearance to this bivalve that in all probability separation 

 will be necessary in the future. 



Loc. — Lochinvar, Hunter River, County Northumberland ; ? Farley 

 Railway Cutting. 



Hor. — Lower Marine Series. 



IV. — riiity!^c]iis)iia oculns, G. B. Sowerby, P. rotnudatitm, Morris, and 

 P. depressmii, Dana. 



When describing Platuscliisma ocuJns, Morris remarked^^ HiQ^t his P. 

 roUiudatunt, might, after all, be but a vai'iety of the first-named. After 

 examining a number of specimens of both, I believe them to be distinct 

 species. 



Platijschisma oculns}^ — The last, or body-whorl is of even and low 

 convexity above, and flatter, or less convex even below, the two surfaces 

 meeting at an obtuse peripheral angle, keel, or edge, over which the lines 

 of growth pass. 



PlatyschisinarotnndatuinM — In this foi-m the body-whorl is distinctly 

 rounded, or convex, above and below, there is no peripheral angle, or keel, 

 and " the inner part of the outer lip appears to have been periodically 

 thickened leaving sulcations in the cast." I have never seen this thicken- 

 ing in any example possessing the definite characters of F. qi'hIhs. 



Flatyschixma depressum}^ — At first sight Dana's figure of this species 

 might be supposed to represent a univalve crashed from above ; such was 

 my opinion previous to receiving a type replica, but the description, " verj' 

 much depressed, almost disk-form," with flattened whorls, " the outer of 

 which has the back subtrnncate " is strictly accurate. 



An example of a very depressed, although imperfect shell from 

 Lochinvar agrees with this description, and is provided with a periplieml 

 band, truncating the entire edge or keel, and evidently corresponding to 

 Dana's expression, " back subtruncate "; in fact, I believe there are traces 

 of this band on the replica. The sculpture of the Locliinvar fossil, where 

 the test is preserved consists of the usual lines of growth, coinciding with 

 the lip margin on the upper surface of the whorl, i.e., curving forwards, 

 but on passing over the truncated band-like periphery they are regularly 



1- Morris — Strzelecki's Phys. Descrip. N.S.Wales, etc., 1845, p. 286. 



'•' Morris — Loc. cit., pi. xviii., fi<^. 1. 



'^ Morris — Lor. cit., pi. xviii., fi<^. 2. 



1" Dana — Wilkes U.S. Explor. Expedii., x. (Geology), 1H49, pi. x., figs. 2a and h. 



