154 SILICEOUS SPONGES. 



t 



The spicules have a brownish granular appearance, and their surfaces resemble 

 frosted sugar. In cases where some of the rays are fractured the cavity of the 

 interior canal with a smooth wall is exposed, and the spicule at first sight looks like 

 an outer crust investing a foreign body, which probably gave rise to the suggestion of 

 Mr. J. Young that it might be an incrusting sponge. The spicules of tliis species 

 are rare, and as they are usually very fragmentary and possess an altogether anomalous 

 appearance, their hexactinellid affinities are not readily recognizable. In the peculiar 

 splitting up of the rays they resemble the complex forms of Holasterella Wnghtii, 

 but they are almost gigantic in comparison, and do not possess the spiral sculpture 

 distinctive of this species. 



The spicules figured have been kindly forwarded to me by Mr. James Bennie, and 

 I have great pleasure in naming the species after him. 



Distribution. Lower Carboniferous : Law Quarry, Dairy, Ayrshire. 



IncertcB sedis. 



Genus AMPHISPONGIA, Salter, 1861. 



Amphispongia oblonga, Salter. (Plate XXXIII. figs. 12, 12 a, 12 b, 12 c, 12 d.) 

 1861. AmjMspongia oblonga, Saltei-, Mem. Geol. Survey of Great Britain, 32, Scotland, 



p. 135, t. 2. f. 3. 

 1877. Amphispongia, Zitt. Studien, I Ab. p. 45, note. 



1879. Amphispongia oblonga, Nicliolson, Manual of Pal. 2nd ed. vol. i. p. 135, f. 33 c, d. 



1880. Amphispongia, F. Roemer, Leth. Geogn. 1 Th. p. 317. 



This species occurs as free, compressed, elliptical masses, rounded both at the base 

 and summit, from 30 to 60 mm. in length and from 8 to 23 mm. in width. The 

 thickness is inconsiderable. The lower portion of the sponge, from one-fourth to 

 one-half its entire length, is composed of closely approximated, straight, elongated, 

 conical spicules, about o mm. in length, and from -75 to 1 mm. in Avidth, arranged so 

 that their rounded summits form the outer surface of the sponge, whilst their obtuse 

 points reach to its central axis. The upper portion of the sponge, immediately above 

 the large conical spicules, consists mainly of cruciform spicules closely arranged in a 

 regular manner, so that one spicular axis is parallel to the compressed surface of the 

 sponge, whilst the other axis is at right angles to it. The rays of these spicules are 

 usually straight, from -6 to "9 mm. in length, and about -12 mm. in thickness. In 

 other spicules five rays (that is one ray at right angles to the other four) are present, 

 and possibly some may possess six rays, but from the condition of the specimens 

 the sixth ray, even if originally present, cannot satisfactorily be ascertained. Very 

 minute filiform monaxial spicules are also present mingled with the cruciform 

 spicules ; and in one specimen there are indications of an exterior surface-layer of 



