458 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



JEREOPSIS FRUTICOSA, new species. 



Plate 43, fig. 3; plate 50, figs. 4, 5, 6, 7, 9. 11, 12. 



One specimen from station D5168. 



Sponge body a fruticose mass consisting of branches which di- 

 verge from the small basal part, anastomosing here and there with 

 one another. Whole mass 55 mm. high, 90 mm. in one horizontal 

 axis, 50 mm. in the other. Branches fundamentally cylindrical, 

 about 7 mm. in diameter; somewhat flattened and lobe-like, espe- 

 cially at the ends. Oscula, 1 mm. in diameter, at the ends, and in 

 rows along the flattened upper side, of the branches; no oscula on 

 under surface of sponge. Sponge hard, stony; brownish yellow. 



Spicules. — 1. Desma. The desma is built not on a calthrops nor 

 a simple triaene but on an amphitriaene, as is shown by the fol- 

 lowering facts. Small free amphitriaenes (pi. 50, fig. 4) about 160 /«. 

 long occur sparingly in the ectosome. In these the axial canal ex- 

 tends through the shaft, and to the tip of each clad. In the young 

 desmas (pi. 50, fig. 5), which occur in the ectosome and which 

 are free or only slightly connected with the skeletal framework, 

 the amphitriaene character is still obvious. Comparison with the 

 first stage (pi. 50, fig. 4) shows that the shaft has increased in thick- 

 ness but not in length. The clads on the other hand have in- 

 creased greatly in length, although the axial canal extends only 

 into the basal part of the clad. In the adult desma (pi. 50, fig. 9) 

 the axial canal s > ystem continues to reveal the original amphitriaene 

 state — that is, it has not changed with the growth of the desma, the 

 canals still extending into the bases of the primary clads. From the 

 end, however, of each branch of the original axial canal system (a 

 system of sharp, distinct lines) there may be traced, after boiling 

 in nitric acid, a pale granular axial streak which extends throughout 

 the branching clad. Comparison with the earlier stages shows that 

 the shaft has continued to increase in thickness but has retained 

 its original length. The clads vary greatly in different spicules and 

 even on the same spicule. The original (primary) clad may remain 

 undivided, or secondary clads may be formed on it, and even tertiary 

 • lads on the secondary. There seems to be a law of growth whereby 

 no unbranched clad shall materially exceed the shaft in length. 

 Zygosis is established through the development of abundant bulbous 

 interlocking projections on the ends and sides of the f< rmmal clads, 

 whether these be primary, secondary, or tertiary (pi. 50, figs. 7, 12). 

 In the adult desma the shaft is 50-60 ij. thick; the meshes of the 

 skeletal framework 90-210 u, in diameter. The peculiar desma of 

 this species and the interpretation of the facts have been discussed 

 in an earlier paper (Wilson 1920). 



