The I'enfjyd Stracfurc of I'ria rlhra.s. — Beechar. 1)1 
lacral petals and between which are puneta that, like those of 
the ambulacral niid-areie, present the appearance of tilled 
pores and are in (luinciinx, thougli forming a simple linear 
series between each two lines; surface of inner, or contiguous, 
halves of interambulacral plates, plain (or at least without 
lines, and with only minute puneta, which, in tiie type-speci- 
men, are mainly obliterated), save near the ends where a 
number of coarse puneta are so arranged as to constitute a 
narrow and indefinite!}' bounded miliary zone. 
Between the anterior and either antero-lateral angle, the 
outline of the test, as viewed from above, presents two trifling 
concavities separated by a broader convexit3^ Between either 
antero-lateral angle and the posterior angle of the same side, 
the outline presents a broad and shallow concavity which cul- 
minates opposite the anterior part of the posterior row of 
plates of that interambulacral field. The bottom of the test 
is not shown in the type, and the posterior border is imper- 
fect, so that the exact form of the latter and the exact posi- 
tion, etc., of the peristome and periproct are unknown. 
3feasH)'enie))fs. — Length of test 105, breadth 83, hight 
(approximatel}^) 8-10 mm. 
Occin'rence. — Preserved in a concretion weathered out of 
the arenaceous shale of the Fox Hills division of the Creta- 
ceous, on the east slope of Shook's Kun. on Piatt avenue, Col- 
orado Springs, Colorado. 
The specimen was collected by Miss Anna Hetherington, 
and by her kindly presented to the writer, who is also indebted 
to Prof. Geo. H. Stone for his first knowledge of the find. 
The writer believes that the genus Sciif.elldster may fairly 
be regarded as a suntlieflc^ or (lenerdlizcd, type from which 
have been evolved Srufclhi on the one hand and iUjuiedsIci- on 
the other. 
FURTHER OBSERVATIONS ON THE VENTRAL 
STRUCTURE OF TRIARTHRUS. 
Bv CiiAiiLES E. UiiiiCHER, New Havcii. ColUl. 
(I'l.ATKS IV AND V.) 
In previous pa[)ers on the ventral structuri' of 'rriarlhriis, 
the anterior antenna', tlioracic legs and appendages of the 
