176 BRITISH PALAOZOIC SPONGES. 
51. Poronenta sparsa, Hinde, sp. nov. Pl. IX, figs. 4, 4a—4e. 
Detached three- and four-rayed spicules, the rays may be either subequal or 
inequal in length, or with two equal rays and one shorter ray, so as to resemble the 
“sagittate spicules” of Haeckel. They are approximately equi-angular, and in the 
same horizontal plane. The fourth ray, when present, is at right angles to the other 
three rays. The rays are smooth and slightly tapering, they terminate obtusely. 
They vary from °15 to °33 mm. in length, and from *025 to ‘062 mm. in thickness. 
These spicules occur in calcareous shales, associated with the fragmentary 
remains of other minute organisms. They are of carbonate of lime and dissolve 
entirely in dilute acid. They have a porcellanic-white aspect by reflected light, and 
become translucent in Canada balsam. Their surfaces are smooth and even, and 
their outlines are as well-defined as the minute perforated plates of Holothurians, 
present inthe same beds. No canals are preserved. Very seldom are the spicules 
complete, one or more of the rays are usually fractured. 
Since it has been definitely proved that Calcisponges are capable of preservation 
in the fossil state, and detached spicules are known to be present in Tertiary 
strata (‘ Quart. Journ. Geol. Soc.,’ vol. xlii, 1886, p. 214), there is no reason why 
they should not occur in the older rocks, as well as other similarly minute and 
delicate calcareous organisms. I do not see any ground for supposing that these 
forms are replaced siliceous spicules, since siliceous spicules of similar dimensions 
very seldom occur detached, and when they are preserved their outlines are usually 
eroded and quite unlike the present forms. 
Distribution.—Lower Carboniferous: Woodend, Cowdens, Fife, Scotland (J. 
Bennie). 
BAD AND DOUBTFUL SPECIES. 
The forms referred to below, from various geological horizons of the Paleeozoic 
series of Britain, have been placed by their authors or subsequent writers in the 
group of Sponges. I have given in each case the reason which has induced me to 
exclude them from this category, based, as far as possible, on an examination of 
the type-specimens which have been described. In some instances it has been 
possible to determine the true systematic position of these fossils, whilst the 
characters of others are too obscure to allow of any identification, and they must 
be at present regarded as incerte sedis. I have not thought it necessary to refer 
