88 TH. MORTENSEN, (Schwed. Südpolar-Exp. 
Tripyliis excavatus Meissner. 1896. Die von Herrn Dr. Plate aus Chile lieimgebrachten Seeigel. Arch. f. 
Naturgesch. I, p. 89. 
— — — 1900. Echinoiden d. Hamburger Magalh. Sammelreise, p. 14. 
Some other less important literary references are given in the two papers quoted 
by Dr. MEISSNER. 
To the descriptions given by PHILIPPI and AGASSIZ I have to add only a few 
remarks. 
The most important feature, the only thing, in my opinion, which justifies mak- 
ing this species the type of a distinct genus, is found in the anterior paired ambu- 
lacra. The petaloid condition does not continue down to the fasciole, the last 4— 5 
ambulacral plates having only small pores; as these plates are about twice as high 
as those above, the non-petaloid part of the ambulacrum inside the fasciole becomes 
about one third of the whole length of the petal. This feature has not been men- 
tioned by either PHILIPPI or AGASSIZ, but in Philippi’s figures 1. a and c (PI. XI) 
it is distinctly seen that the deepened part of the petals ends at a considerable dis- 
tance from the fasciole, and in the fragments of Philippi’s type specimen, which 
Professor LUDWIG has most liberally lent me for examination, I find the same fea- 
ture very distinct. This characteristic feature is thus found equally developed in 
both sexes. (The specimens at my disposal are males.) The posterior ambulacra 
are petaloid in their whole length. — Through the character described this species 
is at once distinguished from the different species of Abatus , with which it otherwise 
agrees in the prominent feature of the petals of the female being developed into 
deep marsupia. The same character distinguishes it from Tripylaster Philippii, with 
which it agrees in the distinctness of the latero-anal fasciole, the central position of 
the apical system and the small spines and tubercles. — One is also reminded of 
Agassizia by this feature of the anterior petals, and it can scarcely be doubted that 
this latter genus is really nearly related to the Brisaster- Abatus group. (That both 
Brisaster and Abatus pass through an »Agassizia»- stage is well worth remembering in 
this connection.) Tr. excavatus was, indeed, referred to the genus Agassizia by 
AGASSIZ & Desor in their »Catalogue raisonné des Échinides». 
As seems to be very often the case among the Irregular Echini, the right an- 
terior side of the test projects somewhat before the left; this holds good for all the 
specimens in hand. 
Of the odd anterior ambulacrum PHILIPPI says that it has »jederseits eine Reihe 
dicht gedrängter Porenpaare, welche, wie gewöhnlich, weit kleiner sind als die Poren 
der paarigen Ambulakra, und sich nach unten zu in eine Reihe einfacher Poren ver- 
wandeln, die sich zum Munde fortsetzt». Contrary to this statement I find the pores 
of the frontal ambulacrum rather distantly placed, much less closely than in the 
Abatus- species; especially towards the fasciole the plates become comparatively high 
