234 ANATOMY AND PHYSIOLOGY 



Pig. 



41. Teifurcated patento-bitebnate. — 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, Bovy^erbank. The skeleton 

 consists entirely of this singularly complicated 

 form of spiculum. 



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



Kg. 41. X 90 linear. 



43. BiANGUiiATED QUADRiKADiATE. — 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 hnear. 

 This singular form is associated with the spiculated 



triradiate one in the skeleton of Hymeniacidon Buck- 



landi, Bowerbank. 



44. Equiangular spiculated-triradiate. — Having the 



three rays in the same plane with the intervening 

 angles equal, and a fourth ray projected from the 

 basal jimction of the radii at right angles to their 

 plane. Hymeniacidon Bucklandi, 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 46 to 60 or 

 70 degrees to the long axis of the shaft. Erom 

 Pachymatisma Johnstonia, Bowerbank. ' X 90 

 linear. 



