PLACOSOMA PARADICTYÜM. V 



ribbed, more prominently on tlie back than on the front. Tt 

 may be described either as a hollow tu])e with the lumen running 

 close under the back surface, or as being grooved on this side, 

 which groove is covered only with a thin sheet of the pith-like 

 tissue. The lumen or the groove is evidently a part of the 

 excurrent canal-system. It opens externally by a limited number 

 of secondary oscula, distributed irregularly on the thin covering 

 .sheet and therefore only on the posterior side of tlie stalk (PI. 

 T., fig. 2.).=^= 



The large, irregularly lobed, basal disc is likewise soft on the 

 surface but internally quite firm. The covered groove of the 

 stalk extends for some distance on the disc- surface, showing on 

 the cover a few more oscular openings. A certain number of 

 other similar but branching canals are seen to ramify on the 

 disc-surface in a vein-like manner. 



The most remarkable features in the organization of the 

 present species lie in the massive development of the body and 

 in the differentiation of a part of the external surface into an 

 area, the frontal lattice, more especially adapted to the reception 

 and passing in of the w^ater than other parts of the same. 



As regards the former point, an analogous case seems to be 

 presented by Malaeosaccus floricomatus, recently described by 

 TopsEXT ('oi). In this interesting Euplectellid the body should be 

 solid and provided with a number of orifices — evidently exhalant 

 orifices or oscula — distributed over the external surface. The 

 describer however leaves margin to allow assumption that perhaps 

 the presence of a shallow hollow at the superior extremity, represent- 



* The small hole seen on tlie front sUle of the stalk (PI. T., fig. 1) is an artifirial 

 perforation. 



