igS FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. VII. 



pies seen from Lake Atitlan were 4-horned, but many, perhaps 

 the majority, from Lake Amatitlan, were 3 -horned. They did not 

 appear to be more slender than the others, however. Kent gives 

 the size as "Length 1-120" to i-9o"-2o8 , to 277 /->.." The 

 examples at hand measured 220 /* long, and 70 , wide at the 

 broadest portion of the body. 



SPONGE IN LAKE AMATITLAN. 



Family Spoiigilidfle. FRESH-WATER SPONGES. 



Spongilla fragilis Leidy. FRESH-WATER SPONGE. 



So far as I was able to discover, there is but one species of 

 Fresh-water Sponge in Lake Amatitlan (none was observed in 

 Lake Atitlan) . This sponge is not very abundant, and is usually 

 found growing on rocks or pieces of wood in the water. It appears 

 on these objects usually as light brown patches, although its color 

 may vary from nearly white to a bright green. The shade of 

 color depends much on the amount of light. The lighter shades 

 are found in the darkest places, and the green color in bright sun- 

 light. 



In general, this sponge bears some resemblance to our com- 

 mercial sponges which grow in the sea. The important differ- 

 ence between those in salt-water and fresh-water is in the com- 

 position of the spicules the harder skeleton mass. The spicules 

 of the salt-water forms are made up of a horny elastic fibre, while 

 those of fresh water are composed of silica. 



The patches of sponges found on rocks along the shore of Lake 

 Amatitlan are subcircular, being thin at the edges and thicker in 

 the middle. 



This sponge is not abundant and is of no commercial value. 

 It is apparently of no economic importance, so far as the fish 

 supply of the lake is concerned. 



This species is very widely distributed over North America, 

 but is not known from bodies of water farther south than Lake 

 Amatitlan. For the identification of this species, I am indebted 

 to Dr. Edward Potts, of Philadelphia. 



