87 
Horizon and Localities . — ^Professor Phillips discovered this pretty 
species at South Pethervvin in Cornwall ; Mr. Clarke has collected it from a 
compact blackish limestone on the hanks of the Murrumbidgee, in the Yass 
District. 
Genus — CONOCAIIDIUM, Bronu. 
CoNOCARDiUM SowERBYi, L. G. dc Koninclc. 
Cardium allforme (var.) Sowerb^^ 1810, Trans. Geol. Soc. London, V (2), pi, 5G, fig. 2. 
Bleurorllljnchus at forme, j. Phillip?, 1810, Pal. Loss. Cornwall, p. 31, pi. 17, fig. 51. 
Shell siih-triangnlar in outline, gibbons, truncate and bounded anteriorly 
by a strongly-marked curved carina ; the anterior surface is heart shaped, 
slightly convex and extending almost to the ventral margin at its loiver 
extremity ; this surface is ornamented with a large number of small conceu - 
trie ribs, which, contrary to those occurring in most other species and 
particularly in those of the type of Conocardium alforme, have their origin 
near the beaks and are parallel to the ribs of the remainder of the surface, as 
has been very clearly stated by Professor J. Phillips. These are fairly regular 
and almost all of the same thickness ; the last only — tliat is to say, those that 
cover the posterior aud gently-gaping portion of the shell — are a little less 
thick and a little more flat than the others. Betw^een these ribs, which are 
about twenty in number, the cellular structure of the shell may be easily 
seen. The probosciform anterior tube appears to bo very short and suh- 
conical. 
1) imensions. — Length, thirteen millimetres; width, fifteen millimetres; 
thickness, eleven millimetres.* 
Melations and Differences . — Several Palaeontologists have confused 
this species Avith Conocardium alforme, SoAverby, Avhich is an exclusively 
Carboniferous species, and AAdiich is distinguished from it easily by several 
characters, the most striking of Avhich are — ( 1 ) the difference of the Avidth, 
Avhich is, proportionally to the length, much greater in the Carboniferous 
species ; (2) the less regular shape and greater number of ribs ornamenting 
*I call “length” the distance between the end of tlie beaks and the most prominent portion of the 
ventral margin ; by ''vidth, 1 mean the antero-posterior diameter ; and by thickness, the line that joins the two 
highest points of the two valves, considered as in position and viewed in profile. 
