REPORT ON THE HEXACTINI^ 41 



individuals measure i cm. on the average in height and about 

 1.2 cm. in diameter, the base being in all cases somewhat 

 larger than the column. Verrill's measurements of preserved 

 specimens are identical with those just given. The tentacles 

 in the most expanded form I examined measured 1.3 cm. in 

 length but in others they were only about half that length. 



Structure. — The column mesoglcea is thin and of a fibrous 

 structure and its inner surface bears a well-developed layer of 

 simple muscle processes. The inner ends of the endoderm cells 

 are heavily laden with dense, black pigment. At the margin 

 the endodermal musculature becomes considerably lower and on 

 the inner wall of the fosse there is situated the sphincter. 

 In the first individual I examined this had the form show^n in 

 Fig. 26 and was situated on the outer wall of the fosse, and 

 from its general appearance I was led to regard it as being meso- 

 glceal and so referred the species to the family Paractidae. 

 The publication of Verrill's description ('99) of the structure of 

 the type and correspondence which I had with him on the sub- 

 ject induce me to examine the sphincter in other individuals 

 and in these I found perfect agreement with what Verrill had 

 described. The sphincter is of the circumscribed sessile form, 

 situated upon the inner wall of the fosse, and has an almost 

 circular form in cross-section ; the mesogloeal lamellae which 

 compose it are rather fine and anastomose more or less in places. 

 It was evident then that the first individual that I examined 

 either had an abnormal sphincter or else belonged to a differ- 

 ent species from the others. The latter possibility seems very 

 improbable on account of the complete similarity in other re- 

 spects and I conclude that the former one is correct. An 

 extension of the area of attachment of the sphincter and a 

 greater development of anastomoses of the lamellae would 

 readily convert the normal sphincter into the condition shown 

 in Fig. 26.^ 



^ This figure is, accordingly, of interest only as representing an abnormality. 

 The plates were unfortunately in process of reproduction before I perceived the 

 error into which I had fallen and it was not possible, therefore, to replace the figure 

 by a represention of the normal sphincter. 



