ORTMANN ! TERTIARY INVERTEBRATES. 
57 
As to the genus Iheringia = Iheringiana, there remains only a single 
character, by which it may be recognized : the considerable narrowing of 
the interambulacral spaces toward the margin of the test (see Lahille’s 
generic diagnosis on p. 14). It is true, this character distinguishes the 
Patagonian fossil from all the known forms of Ec lunar achnius as well as 
Scutella. Nevertheless I do not believe that it is of generic value, since 
this narrowing of the interambulacra is exhibited by several other species, 
only in a less pronounced way. Especially this is true of Echinarachnms 
parma of the Atlantic coast of the United States, of which I have several 
hundred individuals at my disposal. Since this decrease of width of the 
interambulacra is brought about by an increase of width of the ambulacra, 
and the latter is shown in all species of Scutella and Echinar achnius, we 
may put it this way, that in Scutella the ambulacral plates increase sud- 
denly in width from the end of the petals toward the margin, and in the 
Patagonian form this increase is most pronounced, so as to render the 
interambulacra very narrow on the margin, while in other species this in- 
crease goes only so far as to keep the interambulacra at the same width 
from the end of the petals to the margin. Sometimes it causes even a 
slight decrease in width : I have found a slight narrowing of the inter- 
ambulacra in Ech. pavma, Ech . excentricus (California), and very slightly 
in specimens of Scut, interlineata Stps. (Gabb, 1 869, p. 1 1 o) from the 
Pliocene beds of California. 
Lahille compares in this respect Iheringia with Monophora, and says 
(p. 6 of separate copy) that in both this star-like form of the five inter- 
ambulacra, with five sharp points of the pentagram, is very striking. But 
comparing his figures of Monophora (Lahille, 1896, pi. 1-4, especially pi. 
3, f. 36), there is no such close resemblance, Monophora being like Ech. 
parma in this respect. I was able to confirm this fact by comparison of 
an individual of Monophora darwini from the Territory of Chubut, sent 
to us by v. Ihering. 
As Lahille points out, there can be distinguished, in Scutella patagonica, 
two series of forms, one more regularly circular in outline (“mode rotun- 
datus”), the other more dilated and transverse (“mode alatus”). Our 
material also shows these two series, and I should like to make a few 
remarks on them. 
We possess altogether 87 individuals, in which the outline is distinctly 
recognizable. Out of this number only about 16 may be said to belong 
