234 ANATOMY AND PHYSIOLOGY 



FIG. 



41. TRIFURCATED PATENTO-BITERNATE. Consisting of a 



short stout shaft, each end being furnished with 

 three short equiangular radii passing off at right 

 angles to the shaft, and each having its termina- 

 tion trifurcated. X 90 linear. This singular 

 form occurs in the tortuous excavations of pro- 

 bably a small annelid in a soft limestone, the 

 sponge lining the cavities in a manner similar to 

 Hymeniacidon celata, Bowerbank. The skeleton 

 consists entirely of this singularly complicated 

 form of spiculum. 



42. A view of one end of the spiculum represented by 



Fig. 41. X 90 linear. 



43. BIANGULATED QUADRiRADiATE- Having two radii 



projected from a common basal point, in one 

 plane forming an angle of about 90, and the 

 other two projected in a similar manner in an 

 opposite direction in a second plane at right 

 angles to the first one. X 90 linear. 

 This singular form is associated with the spiculated 

 triradiate one in the skeleton of Hymeniacidon Buck- 

 Ian di, Bowerbank. 



44. EQUIANGULAR SPTCULATED-TRIRADIATE. Having the 



three rays in the same plane with the intervening 

 angles equal, and a fourth ray projected from the 

 basal junction of the radii at right angles to their 

 plane. Hymeniacidon BucMandi, Bowerbank. 

 X 90 linear. 



This form is very common in the calcareous 

 sponges, where it appears as a defensive organ. 



CONNECTING SPICULA. 



45. EXPANDO-TERNATE. Having the terminal radii pro- 



jected forward at angles varying from 45 to 60 or 

 70 degrees to the long axis of the shaft. From 

 Pachymatisma Johnstonia, Bowerbank. X 90 

 linear. 



