508 MR, E. W. SnANN ON 



may represent rudimentary siplionozoids. Tlie superficial canals 

 form a dense netwoi'k just beneath the surface of the colony ; 

 their diameter is •044--120 mm. The vessels of the internal 

 system are clearly defined and circular in cross-section, and are 

 fairly numerous. 



Zoochlorell?e are numerous in the superficial canal-system, and 

 occur in less abundance in the interior. They are also found in 

 the endoderm of the poljqis, and extend into the tentacles, 

 occupying even the lumen of the pinnules. 



The spicules are quite characteiistic of the genus Sclerophytum, 

 and indeed only differ from those of Sc. pcdmattim in almost 

 insignificant detail. The little knotted clubs average "1 6 X "034 mm., 

 and the spindles are sometimes only '058 x '015 mm. These 

 minute spicules only occur immediately beneath the surface. 

 The spicules of the coenenchyme are fairly numerous and are all 

 of the tuberculate warted type ; they vary considerably, however, 

 in shape and size. The majority are spindles which narrow 

 rapidly towards their ends to rather acute points ; their measiu^e- 

 ments range from •4x'll mm. to 3"0x45 mm. Irregularly 

 branched forms are by no means uncommon. 



The following considerations are advanced as an apology for 

 the creation of a new species of Sclerophytum based on the 

 examination of a single specimen. 



This colony had been assigned in a preliminary investigation 

 to the species 8g. pahnattmn Pratt (1903), and at first sight this 

 diagnosis appeared perfectly accurate. The external appearance, 

 and indeecl the actual measurements, agree closely with the 

 description of the type specimen. The characters and distribution 

 of the spicules, the well-marked mesenteries and mesenterial 

 filaments, the riidimentary condition of the siphonozoids, the 

 orientation of the canal-systems, and the distribution of the 

 zoochlorellsB, all tend to enhance the resemblance between the 

 two species. It is only when the autozoids are examined tha,t 

 the true specific difference is realized ; those of So. pcdmatimi are 

 distinctly larger than those of Sc. pinnulatum. The characters 

 of the tentacles which foi'm the essential divergence of the two 

 species are tabulated below : — 



Sc. pcdmatimi Pratt. Sc. pinmdattmi, sp. n. 



•7 mm. in length. '55 mm. in length. 



Almost of uniform length. Expanded at distal end. 



Possess a double row of rudi- A single row of free well-deve- 



mentary pinnules down loped pinnules down each 



each side. side. 



Sc. pmoiulal'um could be confounded with no other species of 

 Sclerophytum. At the same time, it is of interest to note that a 

 single row of free pinnules has been recorded on either side of 

 the tentacles of Sc. viride by Thomson and Henderson (1906). 

 The possession of free pinnules, now recorded for two species of 



