CHARACTERISTIC DEEP-SEA TYPES. SPONGES. 



171 



of certain species was often very great, yet the continental fauna 

 of that region is poor when compared with the wealth of species 

 found in the Caribbean Sea and Gulf of Mexico. 



Among the Hexactinellidse one of the most common types is 



Fig. 520. Farrea facunda. -|. 



the variable Farrea facunda (Fig. 520), which occurs either as 

 a simple or a somewhat complicated form ; it is found at depths 





Fig-. 521. Lefroyella decora, f . 



of 300 to 1,000 fathoms. One of the finest, figured by Thom- 

 son, a species called Lefroyella decora (Fig. 521), was dredged 



