52 
PALAEONTOLOGY OF NEW YORK. 
valve is the great post-median depression, which was considered by Mr. Ford 
as' representing a pit for the reception of the pedicle, but the necessity for so 
large an organ in so small and light a shell, as this would imply, does not appear, 
and we have regarded it as the correlative of the central muscular scar in the 
opposite valve. From the anterior end of this scar are two narrow diverging 
furrows, the function of which is not understood, and the analogues of which 
have not been observed in any of the oboloid or indeed among the inarticu¬ 
late brachiopods in general, save in the species Monomerella Greenii, where they 
attain the same relative development as in Elkania. It is possible that these 
furrows are specialized sinuses leading from the genitalia to the pallial vascular 
system, and performed the function of oviducts; their juxtaposition to the pallial 
trunks indicating some such office. Of still further importance in Elkania is 
the narrow furrow in each valve passing around the muscular area just within 
the cardinal margin, terminating laterally in a more of. less well defined scar; 
in other words the first appearance, in the oboloid genera, of a distinctly de¬ 
veloped crescent. As to their appearance in time, Obolus, Elkania and Dino¬ 
bolus are successive. 
If we have, thus, correctly suggested the source and development of the 
platform in the Trimerellids, we are confronted with the interesting phe¬ 
nomenon of a similar resultant attained along different lines of development. 
This may be expressed by the following diagram: 
? 
/Obolella ^ 
-- ( LaJchmina) - 
Lingulella-. 
Dinpbolus- 
■" Lingula-Lingulops - 
- Lingulasma ■ 
Trimerella. 
Monomerella-Rhinobolus. 
It is probable that the progenitor of Obolus will be found in Obolella, or some 
of the closely allied genera, and our present knowledge of Lingulella is such 
that, as elsewhere observed, it must be placed in juxtaposition to Obolella, 
while evincing a deviation toward Lingula. The two are, in all probability, 
but a few removes from their common ancestor, which may be looked for in 
the earliest primordial faunas, unless its existence was limited to obliterated 
