1895.] Sponges: Recent and Fossil. 541 
A thin membrane lines the inner and covers the outer wall, 
pierced by a great number of holes, while the two tissues are 
united by a number of septa. Dr. Dawson compares it to an 
i P: 
Fic. 3. Ethmophyllum. partly restored. Fic. 4. Leptomitus. 
(After Billings.) (After Walcott.) 
inverted cone, formed of carbonate of lime, with its point im- 
bedded in the mud and the open cup above (Fig. 3). The 
lower part is composed of thick plates, enclosing communicat- 
ing chambers. The cup expands above and the spaces between 
the two membranes are filled with sarcode or animal matter. 
Out from the pores projected innumerable pseudopodia, that 
served to convey food to the colony. 
Another one of the sponges from the Lower Cambrian hori- 
zon is a member of the group to which the Glass-rope sponge 
belongs, and it seems to be almost the earliest progenitor of the 
group. It has been named Leptomitus (Fig 4) and consists of a 
long bundle of acicular threads. It represents, possibly, the 
anchoring body of a sponge similar to Hyalonema found at 
present in the eastern seas. In Protospongia is an example of 
a form with a very wide geographical range. It has been 
found in Cambrian rocks in England, in Norway and Sweden, 
in New Brunswick and in Nevada. The extension of this spe- 
cies over so wide an area is indicative of great similarity of 
conditions in widely separated countries. It indicates a sim- 
