24 ^Ir. ^V. J. Sollas on Stauroncma, a new 



2. Stawonema lohat a {nnhi) . 



Form. Posterior mass not extending laterally as far as the 

 lateral edges of the attaehed oscular plate, seldom or never 

 ridged horizontally, usually lobed vertically into two or more 

 diverging processes. 



Oscukti smaller than in S. Carteri. 



Remark. This species is characterized by a more variable 

 and less regular form than S. Carteri. 



EXPLANATION OF THE PLATES. 



Plate I. 



[All the figures of this plate represent the objects of their natural size.] 



Figs. 1 to 4. Stauronema Carteri. 



Ft</.1. An average-sized specimen, anterior aspect: o, oscular plate; 



p, posterior mass ; s, seam or line of division between the two. 

 Fiff. 2. Same specimen as fig. 1, posterior view : b, base ; v, posterior face 



of projecting oscular plate ; e', excurrent canal crossing oscular 



plate, shown ou a fractured surface ; s' s', line of termination of 



posterior mass against the oscular plate. 

 Fiy. 3. A smaller specimen, anterior view, 

 Fiff. 4. Same specimen, posterior view : b, base. 



Figs. 5 to 8. Stauronema Ivbata. 



Fxij. 5. Anterior view of a medium-sized specimen : p', a lobe projecting 

 from the posterior mass. 



Fig. 6. Posterior view of preceding specimen : 5, a fragment of attached 

 " coprolite." 



Fi(j. 7. Posterior view of a specimen showing the diverging lobes of the 

 posterior mass, with the oscular plate visible between them. 



Fig. 8. A very gently curved, almost fiat specimen, showing the fi-ee sur- 

 face of the oscular plate with its pore-areas. 



Fig. 9. Free sponge-plate : l-n, simple outline of its surface ; n n n, ori- 

 ginal margin (the remaining edge is a broken one) ; a, detailed 

 representation of the oscular markings which cover the whole 

 surface of the plate. 



Plate U. 



Fig. 1. Transverse section through StauronemaCarteri : o, oscular plate ; 

 p, posterior mass ; o, 6, & c, directions along which other sections 

 were made through the same specimen — «, longitudinal, 6 t&c, 

 parallel sections ; e&e', excurrent canals. Nat. size. 



Fig. 2. Longitudinal section through the centre of another specimen of 

 <S'. CaHeri : o, jy, e, & e', as in fig. 1 ; d, distal edge of oscidar 

 plate ; ;•, outline in section of ridges formed by an accumulation 

 of the superficial network. Nat. size. 



Fig. 3. Parallel section through the oscular plate along the line c in fig. 1. 

 Nat. size. 



Fig. 4. Skeletal network of oscular plate, magnified from fig. 2 : a, margin 

 of fibre, transparent as far as b, where it becomes granular ; 



