52 



form by the complete absence of the parenchymal oxyhexasters, which are so 

 exceedingly abundant there. 



Most of these 10 specimens fortunately represent different stages of devel- 

 opement, so that they afford an opportunity for ascertaining some facts concern- 

 ing the developement, at least the post-embryonic developement in Hexactinellids, 

 of which so very little is known. Before entering on this subject, however, I 

 will give a diagnosis of this new species by describing its shape, its structure, 

 and particularly its spiculation. 



One of the specimens, the lower end probably of a fuUgrown individual, 

 is 8 cm. long. The upper part has the appearance of a funnel-shaped tube, 

 3 cm. wide. Below, it passes into a root-tuft, destitute of the soft parts (pi. 

 X. f. 5). 



The specimen next in age which is fairly complete — only the terminal sieve- 

 plate and some parts of the lateral wall being lost — is, exclusive of the root-tuft, 

 11 cm. long. The body is, one-third of its length from the top, 25 mm. broad, 

 and tapers slightly towards the upper, more considerably towards the lower end 

 (pi. X, f. 6). 



A third, still better preserved specimen, represented in fig, 4 on plate X, 

 is, exchisive of the root-tuft, 9 cm. long and has a maximum breadth of nearly 

 2 cm. The terminal sieve-plate i2 well preserved and measures 10 mm. in 

 diameter. 



The fourth specimen is, exclusivf^ of the root-tuft, 75 mm. long and up to 

 15 mm. broad. 



Then there are five more or less injured specimens, 4-5 cm. long and about 

 1 cm. broad (pi. X, f, 2, 3). 



The smallest specimen is, exclusive of the root-tuft, 3 cm. long and through- 

 out its length pretty uniformly 5 mm. broad (pi. X, f. 1). 



In the external appearamce and in the macroscopic characters of its internal 



structure, EiqylecteUa dmpJex is very similar to the doubtless closely-allied 



species Euplectella ovmni Marsh, and Herkl,, which was first described in 



.detail and figured by W. Marshall in 1875 in his " Untersuchungen iiber Hexac- 



tinelliden" (Zeitschr. wiss. Zool. Bd. XXV, Suppl. Taf. XII D). The tubular 



body is in Eupledella simplex, as in E. oweni, ex,tended a little in the middle and 



very slightly constricted above. The upper end is for some distance cylindrical. 



The wall of the sponge-tube is pretty thin, and perforated by numerous, circular 



parietal apertures, arranged fairly regularly in longitudinal and transverse rows. 



A collar surrounding the terminal sieve-plate as in E. aspergilhim, is absent in 



E. simplex as in E. oioeni. Its place is taken iii E. simplex by the thickened 



maro'in of the terminal face, from which a verticil of short, oblique marginal 



spicules visible to the naked eye, protrudes obliquely. 



/ 



