Sponges from the Atlantic Ocean. 209 



modified in form in the deep-sea sponges, may be under- 

 stood. 



The equianchorate, then, of Halichondria incrustans consists 

 of a shaft and three arms or hooks of equal size at each end, 

 whence its specific designation (Plate XIII. fig. 1, a,b, c). The 

 shaft is curved bow-like equally (fig. 1, a, d), and the three 

 arms recurved towards the concavity of the shaft (fig. 1, b, e,f). 

 Two of these arms are lateral (fig. 1, b,f), and the other ante- 

 rior or in front (fig. 1, be, ae) ; hence the back of the shaft 

 forms a continuous and uninterrupted curve (fig. l,d). All 

 three of these arms are attached to the shaft by falciform ex- 

 pansions, extending between the shaft and the arms respectively 

 (fig. 1, ag,ch), which expansions will be termed in the sin- 

 gular number the " falx," and in the plural "falces;" and 

 while the two lateral arms, being opposite to each other, thus 

 present a wing -like appearance (fig. 1, ch), the anterior one 

 being single, median, and in front, presents a linear form ; but 

 in all the falx is more or less retracted and web-like towards 

 the end of the shaft (fig. 1, a g). 



As the anterior arm of the anchorate in other sponges fre- 

 quently presents a petaloid or tongue-shaped form of extreme 

 thinness, while the linear element, when it remains in this 

 form, represents the midrib of a leaf, but as often is retracted 

 into an elliptical or circular body, which, at the base of the 

 petaloid expansion, is joined through the intervention of the 

 falx to the shaft, we shall call this the " tubercle " (fig. l,bt, 

 and fig. 4, e). 



Tims we have to remember the " shaft," the " lateral " and 

 " anterior arms " respectively, the " falx," and the " tubercle " 

 for this complicated little spicule. 



I should also here add that, in the anchorate of Halichondria 

 incrustans, there are four lateral convex aliform expansions 

 of the shaft itself, viz. one on each side towards the ends, thus 

 causing the shaft to present a constricted form in the centre 

 when viewed anteriorly or posteriorly (fig. 1, b & c). These ali- 

 form expansions will also be seen, by-and-by, in the ancho- 

 rate of Chondrocladia virgata and other deep-sea sponges. 



In my last communication to the ' Annals ' (I. c.) it will be 

 observed that I have figured three forms of flesh-spicules as 

 common to Halichondria ozgagropila, Johnston [Esperia o?ga- 

 gropila } Gaiter) ; and it will also be found that the two additional 

 ones (viz. the "tricurvate" and the "bihamate") are as fre- 

 quent in their occurrence in many other sponges as the " an- 

 chorate " itself, but, being very simple in construction, they do 

 not require a detailed description like the anchorate. In the 

 communication to which I have just alluded it will further be 



