176 BRITISH PAL/EOZOIC SPONGES. 



51. Pbeonella spaesa, Einde, sp. nov. PL IX, figs. 4, 4 a — 4 e. 



Detached three- and four-rayed spicules, the rays may be either subequal or 

 in equal 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 "06.2 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 in the 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 Palasozoic 

 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 incertce sedis. I have not thought it necessary to refer 



