56 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
have been united by Lahille in his monograph on these forms into one 
species, for which he creates the new genus Ikeringia. This generic name, 
being preoccupied by Keyserling in 1891, has been changed by Berg 
(1898, p. 16) into Iheringiella (non Iheringella Pilsbry, 1893), and again 
into Iheringiana (Berg, 1898, p. 41), and finally Lahille himself (1899, p. 
5 of separate copy) has changed it into Iheringina. 
After a careful study of our rich material I am prepared to accept Lahille’s 
view as to the identity of these supposed two species, as well as his views 
on the respective value of the genera Echinarachnius and Scutella , but I do 
not think that the Patagonian fossil ought to be placed in a separate genus 
{Iheringia = Iheringiana Berg) ; I prefer to leave it with the genus Scutella . 
In discussing the differences of Echinarachnius and Scutella , Lahille 
has overlooked the fact that A. Agassiz (1872, p. 315) has given a charac- 
ter, by which the subgenus Echinarachnius may be distinguished from the 
true Scutella , viz., the arrangement of the pillars in the interior of the test. 
In Echinarachnius (as well as in Dendraster and Scaphechinus ) the pillars 
are more or less concentric with the edge of the test, while in Scutella they 
recall more the stellate arrangement of Mellita. This is said to be the 
only ground on which Echinarachnius might be separated from Scutella. 
I have tried to verify this character, but did not meet with much success. 
Failing to find any good figures representing the interior of the test of 
Scutella , I have compared that of Mellita as given by Agassiz (1872, pi. 
12a, f. 1-4) with those of the interior of Echinarachinus (Agassiz, pi. 13a 
and 1 id, f. 45) and of Iheringia (Lahille, 1898, pi. 2, f. n, 12), and do 
not find any essential differences, except that in Mellita this system of 
pillars is more complex, but it shows nevertheless distinctly a concentric 
arrangement near the edge (especially fig. 4 on pi. 12a of Agassiz). As 
to Scutella, I have chiefly compared the account and figures of Scut, sub- 
rotunda given by Quenstedt (1875, p. 544, pi 83, f. 2, 4), and also do not 
find any differences from Echinarachnius ; indeed, the different sections 
given by Quenstedt in fig. 4 render it beyond doubt that the concentric 
arrangement of the pillars in Scutella agrees with that of Echinarachnius. 
Thus it appears that even this character does not permit a separation of 
Echinarachnius from Scutella, both genera (or subgenera) being practically 
identical ; all the characters given as distinctive (outline, ambulacral fur- 
rows of lower side, position of anus, shape of ambulacral petals) are only 
of specific value. 
