426 Prof. J. Young and Mr. J. Young on 



Hyalonema {Serpida) parallelum, M'Coy." Soon afterwards 

 we found hexactinellid spicules on the same slab with II. 

 paraUelum (PL XIV. fig. 4), and rods identical with that 

 fossil terminating in anchoring spicules (figs. 15, 16, 17). 

 Nail-like and sexradiate spicules we had previously found in 

 a matted mass (fig. 30). 



The plates accompanying this paper were prepared early in 

 the present year, and therefore do not include all the varieties 

 which have since come into our possession through the 

 kindness of Messrs. Smith and Armstrong. Mr. II. J. Carter, 

 who published a preliminar_y note in the 'Annals' for Septem- 

 ber, and with whom we have since been in correspondence, 

 has courteously postponed the publication of his second com- 

 munication till we have made public the results at which we 

 had previously arrived. The present communication has been 

 delayed in the hope of obtaining further information as to the 

 geological and chemical conditions under which the strata 

 were deposited and subsequently altered ; but as the accumu- 

 lation of this kind of evidence is necessarily a slow process, 

 we do not think it right longer to hold back our notes. We 

 shall commence with the form which first secured our atten- 

 tion. 



1. Hyalonema Smithu, Y. & Y. 



Serpula parallela, M'Coy. 

 Acanthaspongia Smithii, Y. & Y. 



Sponge-body unknown. Spicules of three kinds :^a, nail- 

 like, some with four tapering, generally unequal, arms, a fifth 

 projecting at right angles to the^e, others approacliing the 

 sexradiate type by the projection of a rounded, sometimes 

 stalked, process opposite to the fifth ; J, sexradiate, with the 

 arms of various sizes but always projecting, and of various 

 number, either by reduction or by the adhesion of other 

 spicules ; c, long, smooth, slender, tubular rods (the Serpula 

 paralleluj M'Coy), tapering towards the extremity and ending 

 in the anchoring booklets, the tip of the rod being either not, 

 or only slightly, inflated. The rods are of unknown length, 

 the longest fragments found at Trearne being 12 inches, and of 

 various thicknesses from one fortieth of an inch to nearly a line 

 in diameter ; the central canal is capillary, making up from one 

 sixth to one eighth of the total diameter. The fragments 

 bearing the anchoring booklets are from one eighth to five 

 eighths of an inch in length. The sexradiate spicules range from 

 one fourth to one eighth of an inch in diameter; the nail-like spi- 

 cules from three eighths to one sixteenth of an inch in diameter. 



Locality. Cunningham Baidland, Dairy, Ayrshire. 



