312 
M. K. A. Zittel on Fossil Tetractinellidce. 
layer. Oscula, pores, and canals are distinctly visible only in 
fresh specimens furnished with sarcode. Skeleton with no 
horny fibres, consisting of irregularly intermixed spicules of 
various forms. The true skeletal spicules are chiefly quadri- 
radiate; but one ray is very frequently developed into an 
elongated shaft, or reduced so as to form a button-like swelling, 
or so completely that a simple triradiate results. Certain arms, 
or sometimes all the arms, of the quadriradiates may fork once, 
or rarely more than once. Simple bacillar spicules also occur 
more or less abundantly; and these, as well as the tri- and 
quadriradiates, are generally of different sizes. Besides the 
true skeletal corpuscles there are great numbers of minute 
flesh-spicules, distinctly recognizable only under a high 
power; and these are of very various forms and may chiefly 
be employed for the discrimination of the species. The flesh- 
spicules are sometimes small, spinous, straight or curved 
bacilli, sometimes spherical spinous stars, sometimes minute 
spherules like those of Geodia , sometimes smooth elliptical 
lamellas, &c. In fossil specimens the flesh-spicules are not 
preserved, any more than those of the Hexactinellidge and 
Lithistida?. 
In examining the splendid sponge-material from the Upper 
Cretaceous of Ahlten, in Hanover, which was entrusted to me 
by my friend Prof, von Seebach, I met with two insignificant¬ 
looking nodular fragments of small size, which I at once re¬ 
cognized as typical Pachastrellce , when they proved, after 
treatment with muriatic acid, to be composed of isolated 
quadri- and triradiates. As objects for comparison Mr. Carter 
had sent me the existing species, Pachastrella abyssi , Schm., 
and P. geodioides , Cart., and also two fragments from the 
Upper Chalk of Flamborough Head, the last of which, not- 
Avdthstanding their unfavourable state of preservation, exactly 
agreed with the form from Ahlten. 
Pachastrella primceva, Zitt., 
consists principally of very large, stout, simple quadriradi¬ 
ates (cross-spikes), the thick arms of which gradually dimi¬ 
nish in thickness from the centre to the ends, and terminate 
in points. Sometimes the arms are of unequal length and one 
or more of them curved; more rarely certain arms, but never 
all of them, are divided at the ends into two or more points. 
Among these large bodies there lie numerous small regular 
quadriradiates, as well as isolated forked anchors, with a 
simple shaft and trifurcate prongs. Bacillar spicules pointed 
at both ends also occur, but rarely. 
[To be continued.] 
