240 College of Forestry 



smooth or sparsely spined amphioxi. The first mentioned cover 

 the foraminal side of the gemmules and the others are asso- 

 ciated with the other side which is next to the substratum. 



Gemmules are abundant and form a pavement layer on the 

 substratum and are surrounded and bound together into a 

 firm crust by a cellular pneumatic layer which is closely 

 crowded with spicules of which the majority are of the short, 

 stout amphistrongylous type. 



The material available consists of a few dry colonies borne 

 on the surface of stones. 



Holotype. Cat. No. 9190, U. S. Nat. Mus. Paratypes in 

 the collection of The New York State College of Forestry, 

 No. — , and in that of the writer. 



At a first glance one might assume that the colonies belong 

 to S. fragilis, but an examination of the spicules under the 

 microscope at once shows the wide difference between the 

 two species, since in S. fragilis the skeleton spicules are smooth 

 while in the new form they are profusely covered with small 

 spines except near the ends (fig. i). Another notable differ- 

 ence js found in the striking difference between the gemmule 

 spicules (fig. 2) on the foraminal surface of the gemmules, 

 and the more slender, elongate, sparsely distributed ones on 

 the surface next to the substratum. 



Figures 3 and 4 illustrate some of the more usual forms 

 among the latter and one can find various sorts of intergrades. 



In S. fragilis the spicules in the thin layer between the 

 pavement layer gemmule aggregates and the substratum are 

 somewhat more sparsely distributed than on the opposite 

 side of the gemmules ; the spinous amphistrongyli are in some 

 specimens somewhat more elongate and slender, and there 

 are sometimes slender amphioxi which are considerably smaller 

 than the skeleton spicules ; but there are few or no such 

 spicules as are represented in figure 4; and in most speci- 

 mens of 6^. fragilis examined by the writer, there is but slight 

 differentiation between the spicules from the different surfaces 

 of the gemmule layers. 



In vS". Iieterosclerifera the length of the skeleton spicules 

 is .22-.27 mm. with an average of about .25 mm. and the 



