74 THE PALEONTOLOGY OF MINNESOTA. 



LAnomalospongla 



occur in Silurian strata near Edinburg, Scotland.* From Hinde's description and 

 remarks on the only known species, A. oblonga Salter, (Catal. Foss. Sponges, Brit. 

 Mus., p. 154, 1883) we learn that the lower half of the sponge is composed of "closely 

 approximated, straight, elongated, conical spicules, about 3 mm. in length, and 

 from .75 to 1 mm. in width, arranged so that their rounded summits form the outer 

 surface of the sponge, whilst their obtuse points reach to its central axis." The 

 upper part of the sponge is said to consist of small cruciform and five- (possibly six-) 

 rayed spicules, and of very minute filiform mon-axial spicules, while "in one speci- 

 men there are indications of an exterior surface-layer of filiform spicules regularly 

 arranged in the direction of the length of the sponge." The spicules seem in no 

 case to have been organically attached to one another, nor are canals present, but a 

 narrow tubular cloacal cavity was detected in the lower part of a few specimens. 



Salter regarded the spicules as triradiate, and Hinde admits that when not 

 detached from. the mass "only casts of three rays are exposed." The surface of the 

 upper part, as figured by Hinde (op. tit.) resembles part of the surface of casts of 

 species of Ischadites so closely that it is a matter of surprise that so keen an observer 

 as Dr. Hinde failed to make a note of it in his memorable work on the Receptaculitidce. 



The supposed surface-layer, with its longitudinally arranged filiform spicules, 

 causes me to think it possible that the horizontal rays in A. oblonga may really be, 

 as in Anomalospongia, three in number, with the longitudinal ray the strongest. At 

 any rate it would be well to re-examine Amphispongia oblonga in the new light fur- 

 nished by Anomalospongia reticulata. The club-shaped spicules of the lower part of 

 the sponge are too much like the vertical ray of the spicules of Anomalospongia to be 

 without significance entirely. My impression is that the lower spicules of Amphi- 

 spongia are not really mon-axial, but will be found to have head rays similar to if not 

 precisely like those of Anomalospongia. Further, is it not possible that the same kind 

 of entering rays (only smaller, perhaps,) occur in the upper part of the sponge as 

 well, being covered thei-e by the matrix which may intervene at a constriction just 

 beneath the horizontal rays, and thus present to view the casts of the latter only ? 

 Again, it is possible that the so-called "upper part" of A. oblonga may really owe its 

 comparative smoothness to the development of a dermal layer consisting of small 

 cruciform and filiform spicules. But this is only speculation. What is wanted are 

 facts showing the true condition of things in Amphispongia, and I hope some of our 

 British paleontologists will favor us with a full account of them. In the meantime 

 we can use only the close approximation and the shape and size of the spicules of 

 the lower part in showing the relationship which I am satisfied will sooner or later 

 be proven to exist between the two genera. 



*T)ie specimen- lire moulds in slialy rock merely, the sponge spioules themselves having beeu dissolved completely 

 away. 



