334 Mr. A. Hancock on the Excavating Powers of Sponges ^ 



enlarged extremity ; and sometimes the pointed end is a little 

 recurved^ giving to the spicnlum a slight S-like twist. 



This species is common on the coast of Northumberland, where 

 almost every piece of limestone at low-water mark has the sur- 

 face riddled by it : it likewise occurs in the shell of Fusus antiquus 

 and Buccinum undatum. I have obtained it also in oyster- shells 

 from Prestonpans. The walls of the burrows of this form are 

 strongly punctured, and every here and there are drilled with 

 small conical holes. When in the thin shell of Fusus or Bucci* 

 num, the branches are all confined to the same plane, and then 

 this species has considerable resemblance to a Gorgonia. But 

 when it takes up its abode in limestone, the branches frequently 

 pass vertically to some depth into the substance of the rock, 

 giving to the sponge a very complicated structure. 



In old specimens the branches become less regular, increasing 

 much in thickness and number until very small spaces divide 

 them : the external walls are now liable to give way, and the 

 sponge being thus exposed must either perish or sink deeper 

 into the matrix. 



C. radiata. PI. XV. fig. 3. 



Sponge delicately branched in a radiating manner; the branches 

 being y^g th of an inch thick and divided at unequal distances into 

 elongated lobes : terminal twigs simple, minute, linear : papillae 

 rather variable in size, frequently very small, placed in a single 

 close-set row along the branches ; in the central axis where the 

 branches unite there is one much larger than the rest. Spicula 

 ^^th of an inch long, stout, straight, frequently a little bent ; one 

 end with a large ovate head widest at its junction with the shaft, 

 which is a little constricted at the point of union, and from which 

 it is strongly defined by a dusky shadow. 



This form buries itself in the shell of Triton variegatus, and is 

 easily recognized on the surface by the radiating lines of minute 

 close-set papillary punctures. It is very destructive to the shells 

 it attacks : at first it is composed of a few simple radiating 

 branches ; these afterwards enlarge, and send off" lateral shoots 

 which anastomose with the adjoining branches, and ultimately 

 fuse, as it were, towards the centre, which becomes one mass of 

 sponge frequently an inch wide ; all the shell, of course, at this 

 part being entirely removed. 



C. gracilis, PI. XIV. fig. 7. 



Sponge composed of a few long, slender, linear branches, rarely 

 if ever anastomosing, extending in length upwards of 5 inches, 

 and only y^^th of an inch thick, with a few distant, indistinct 

 constrictions indicating an approximation to a lobed structure : 



