A Sphinctozo(()i Calcisponge. — Clarke. 891 
grounded to be disparaged, but their further inference that 
the existence of such tissue signifies relationship to the corals 
must be reconsidered in the light of the fact that vesiculatiou 
of exoskeletal tissue is the undoubted accompaniment of pei-- 
manent or temporary fixation, as evinced by the brachiopods, 
gastropods, lamellibranchs, bryozoans and the corals them- 
selves. 
In comparing the structure of these fossils with the various 
generic divisions of the sphinctozoans erected by Steinmann. 
it is seen that they belong to this author's family, Sphwrosi- 
phonidfe, whicli embraces the genera Barroisla, Munier-Chal- 
mas (Aptian), jfc^^oj'j/ocfgZ/fl, Steinm, (St. Cassian), Thalamo- 
pora, Roemer, Ambl ysiphonelld, Steinm., (upper Carbonifer- 
ous, Sebargas) and ^^eftrrrr/o-sic/, Steinm., (upper Carboniferous, 
Sebargas). All of these forms possess a more or less com- 
plete central cylinder, and in the genera Barro/sia, Ambli/- 
siphonella and Sehar(jasiu. the generic difference is very ob- 
scure; in the last two the sponge has a much more strongly 
annulated exterior than in the first, and between Barroisic 
and iSebdi-fidsia, and Ambhjsij^Jwnella , there is a palpable dif- 
ference in the size of the meshes or pores of the skeleton, 
these being larger in the two former. On further investiga- 
tion, it may prove difficult to maintain more than a specific 
difference in the forms referred to Sebarf/asia and Aniblysi- 
phoneUa, and to the former we should be disposed to ascribe 
the Nebraska species, on account of closer agreement in the 
size of its pores, with the single described form of Sebargas ki . 
Waagen and Wentzel have, however, referred the Salt- 
Range species which are, structurally, like ours, to the genus 
Amblysi.j)honella from which they depart, in the presence of 
vesicular tissue, quite as widely as from Sebaryasia. In def- 
erence to this employment of the term, we therefore designate 
the Nebraska species as AmblysiphoneJIa prosseri. 
EXPLANATION OF PLATE. 
Amblysiphonella prosseri Clarke. 
Upper Carboniferous (Webaunsee formation), Nehavvka and Weeping 
Water, Nebraska. 
Fj(;ures 1 and 2. Opposite sides of a m-arly t-ntire specimen, show- 
ing the aperture. 
Figure 3. A more slender and more strongly annulated specimen. 
