112 BIOLOGICAL SURVEY OF 



Polymastia Sp. ? 



This form was taken at Stations D 19, 90, 101, 135. 



There are six specimens of this form, which has a marked 

 tendency to be circular. These specimens range from 5 mm. 

 to 50 mm. in diameter. The largest specimen has between 

 85 and 90 papillae, which do not exceed 8 mm. in height. 

 These papillae, when growing very near each other, have a 

 tendency to coalesce. The diameter of these papillae does not 

 exceed 4 mm. In some of the specimens a few of the papillae 

 are curved at their distal ends; thus extending roughly 

 parallel to the general surface of the sponge. There are no 

 visible openings on the distal ends of the papillae. The thick- 

 ness of the specimens varies with its size; the largest speci- 

 men is 15 mm. in height. This form is more massive and 

 robust than P. rohusta. Around the edges, which are below 

 the general level of the sponge, there is a marked hispidity 

 which is quite noticeable as a dirty-brown rim due to the 

 adherence of fine particles of silt. In living condition this 

 sponge is a bright yellow, often an orange yellow. 



Skeleton consists of stout fibers (.081 to .203 mm. in diam- 

 eter) perpendicular to the surface. Unlike P. rohusta, these 

 fibers only occasionally extend into or through the cortical 

 layer. 



In the outer part of the cortical layer there is an abundance 

 of small spicules, closely packed and generally perpendicular 

 to the surface beyond which they project very slightly. Thus, 

 in a profile view under the microscope there is discernible a 

 slight hispidity, which otherwise is not noticeable. 



In the inner part of the cortical layer the spicules are larger 

 and, in general, arranged parallel to the surface, but other- 

 wise there is no definite arrangement. 



Spicules. 1) Cortical tylostyli (a) from the dermal layer 

 of the cortex. These spicules are usually curved, stout, and 

 strongly fusiform with well-developed heads. Many of these 

 spicules are subtylostyli, with a distinct inflation just median 

 to the end of the spicule. These spicules vary in length from 

 .161 to .226 mm. in length, and are .0073 to .0094 mm. at their 



