OP THE SPONGIADjE. 47 



them either in the form of a simple attenuated termination, 

 as represented in Fig. 140^ Plate VI, or it expands laterally 

 and forms a third intermediate tooth of a hastate form, 

 as represented in Pig. 147, Plate VI. In either of these 

 cases I therefore designate the spiculum as tridentate. In 

 other cases, the lateral expansions forming the palm are 

 continued along the shaft of the spiculum to nearly, or 

 quite, the full extent of the palm, forming a single, 

 undivided, more or less concave termination, as in Fig. 138, 

 Plate VI. I propose, therefore, to designate this form as 

 palmato-anchorate ; and intermediate forms between the 

 decidedly dentate or palmate ones vpould be designated as 

 tridentato-palmate (Fig. 138, Plate VI), the palmate form 

 being in excess of the dentate structure ; or palmato-tri or 

 bi-dentate, when the teeth are in the ascendant. 



Generally speaking, the ends of the shaft of each 

 anchorate spiculum either become obsolete at the base of 

 the teeth, as in bidentate forms, or they are continued in a 

 regular curve, forming the third tooth, as in the tridentate 

 form ; but in some cases, as in Halichondria plumosa, 

 Johnston, the shaft appears to terminate abruptly at each 

 end, aud the palms or teeth are projected towards each 

 other at a sharp angle to the ends of the shaft or bow 

 of the spiculum : in this case we should term the spiculum 

 angulated anchorate, as represented in Figs. 141, 143 and 

 143, Plate VI. 



The anchorate spicula are not, like the acerate, acuate 

 and other simple forms, of the same shape, or nearly so, 

 from the commencement to the termination of their 

 growth, but, on the contrary, they are . developed pro- 

 gressively. 



In a new species of Halichondria, for which I am 

 indebted to my late friend, Mr. Thomas Ingall, the 

 course of their development is displayed in a very interest- 

 ing and instructive manner. The first condition in which 

 we detect them is in the form of an exceedingly slender 

 and , elongated simple bihamate spiculum, which is readily 

 distinguished from the true bihamate form by the straight- 

 ness of the shaft, the comparative shortness of the hami, and 



