THE EXCAVATING SPONGES. 351 



the wide extremity in connection with the shaft : the other form, 

 which is scarcely one-fourth the length of the pin-like kind, is 

 rather stout, cylindrical, arched, worm-like, undulated frequently 

 three or four times, with the extremities obtuse : both kinds are 

 numerous. 



Two specimens of this well-marked species have occurred, both 

 in a species of Chama, in my cabinet. The spicula are very 

 characteristic : I have met with no other species which has the 

 undulated or worm-like kind, and the stout shaft and broadly 

 ovate head of the pin-like form are very striking. The surface 

 of the excavations is strongly shagreened and exhibits a few 

 scattered punctures. 



C. mamtlanensis. PI. XVII, fig. 1. 



Sponge when dried of a soiled brown or pale drab colour, made 

 up of a vast number of minute lobes about -roth of an inch wide, 

 irregularly rounded, united by very short constricted stems, and 

 so crowded that the mode of branching is perceptible only at the 

 margin of growth, where it is seen to be dichotomous, the ter- 

 minal twigs being rather short, delicate, and obtuse : papillse 

 very numerous and minute, distributed without apparent order, 

 sVth of an inch wide; there are a few larger ones scattered amidst 

 the others and about three times their size. Spicula of three 

 kinds : the first is pin-like, ry-s-th of an inch long, with the shaft 

 straight, delicate, and gradually tapering to a fine point at one 

 end, the other exactly terminated by a large oval head, within 

 which a cavity is distinctly seen : the second kind is fusiform, 

 about half the length of the former, most minutely spined, pretty 

 regularly arched, and with both ends sharply pointed : the third 

 form is quite minute, not more than -rsVoth of an inch long, 

 cylindrical, sharply bent in the centre, roughened, or minutely 

 spined, and with the extremities obtuse. 



I have seen but one specimen of this species ; it has over-run 

 the entire surface of a Purpura, from Mazatlan, presented to the 

 Newcastle Museum by Dr. P. P. Carpenter. The surface of the 

 burrow is strongly shagreened. 



