Pio. 



OF tna SPONGIADiE. 229 



SP1C0LA OS' THE BKELEtON. 



1. Agerate. — 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 

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

 portions. 



2. In 'Spongilla fluaviatilis it is much shorter and stolitter. 



X 160 linear. 



3. PusiEORMi-ACERATE. — Having the greatest diameter 



at the middle of the shaft, and decreasing gradually 

 to each acute termination. HalicJiondria coccinea, 

 Bowerbank. X 160 linear. 



4. Infjlato - FusiEORMi - ACERATE. — Fusiforifti - acerate, 



with a globular inflation at the middle of the 

 shaft. This form of spiculum is abundant in the 

 skeleton of Isodictya «i?o?«a/«, Botverbank. It is 

 sometimes extremely fusiform in shape. X 160 

 linear. :M 



5 Ineqtji- ACERATE VERMicuLoiD. — YxonS HymerapUa 

 vermiculata, Bowerbank, Shetland. X 175 linear. 



6. AcuATE. — Of the same diameter from the hemi- 



spherically-terminated base to near the acutely- 

 terminated apex. Hcdiehondria Alderi, Bower- 

 bank. X 160 linear. 



7. Achate. — ^From Hymeniacidon caruncula, Bowerbank. 



X 160hnear. 



8. FusiEORMi-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. 



