OF THE SPONGIAD^E. 229 



SPICULA OF THE SKELETON. 

 FIG. 



1. ACERATE. Of the same diameter for the greater 



part of the length of the shaft, but decreasing 



equally near each termination, and ending acutely 



at both. X 160 linear. 



The proportions of length and diameter vary to a 

 considerable extent in this form. In Halichondria 

 panicea, Johnston, it is of about the medium pro- 

 portions. 



2. In Spent/ilia fluaviatilis it is much shorter and stouter. 



X 160 linear. 



3. FUSIFORMI-ACERATE. Having the greatest diameter 



at the middle of the shaft, and decreasing gradually 

 to each acute termination. Halichondria coccinea, 

 Bowerbank. X 160 linear. 



4. INFLATO - FUSIFORM: - A CERATE. Fusiform! - acerate, 



with a globular inflation at the middle of the 

 shaft. This form of spiculum is abundant in the 

 skeleton of Isodictt/a anomaJa, Bowerbank. It is 

 sometimes extremely fusiform in shape. X 160 

 linear. 



5 INEQUI- ACERATE VERMICULOID. From Hymeraplda 

 vermiculata, Bowerbank, Shetland. X 175 linear. 



6. ACUATE. Of the same diameter from the hemi- 



spherically-terminated base to near the acutely- 

 terminated apex. Halichondria Alderi, Bower- 

 bank. X 160 linear. 



7. ACUATE. From Hymeniacidon carnncula, Bowerbank. 



X 160 linear. 



8. FUSIFORMI-ACUATE. Having the largest diameter 



near the middle of the shaft, and decreasing thence 

 gradually towards the hemispherical base and the 

 acute apex. Halichondria crustula, Bowerbank. 

 X 160 linear. 



