THE MOUNT DESERT REGION 79 



as Woods Hole. Chalina arbuscula (Verrill) has been re- 

 corded from Vineyard Sound, but has never been taken else- 

 where. Ten species — Gellius flagellifer, Gellius laurentinus, 

 Asbestopluma cupressiformis, Artemisina arcigera, Clathria 

 delicata, Phakellia ventilahrum, Suberites ficus, Tentorium 

 semisuberites, Reniera rufescens, and Reniera mollis — have 

 been reported from the Gulf of St. Lawrence, but from 

 nowhere farther south. However, the sponge fauna of the 

 Atlantic coast of North America will have to be much more 

 carefully studied before much can be said about the distribu- 

 tion of these forms. 



The classification of the Monaxonida is difficult because of 

 the few characters of taxonomic value these forms present. 

 Those characters which are of use to the systematist do not 

 appear to be so definitely fixed as in some of the higher groups 

 of organisms and seem capable of extreme modification as a 

 result of environmental influences. In this order of sponges 

 the external form is almost useless as a character of diag- 

 nostic value. This is especially true of the shallow-water 

 forms, although in some cases individuals of the same species 

 have a similar external form as shown by Eumastia sitiens 

 and Suberites concinnus. However, the external form and 

 mode of growth are relatively unimportant as a guide to 

 classification, and in this paper they are not treated in detail. 



The arrangement of the skeleton is likewise of little value 

 in many cases as a criterion for distinguishing genera and 

 species, as this character may vary greatly in different indi- 

 viduals and even in different parts of the same individual. 

 Lundbeck records the occurrence in the Danish seas of speci- 

 mens of Chalina oculata, which have polyppicular fibers pres- 

 ent in great numbers instead of the characteristic unispicular 

 ones. 



The amount of spongin present has been used by many 

 workers as a distinguishing trait, but this has likewise been 

 shown to be of little value, as the degree of spongin develop- 

 ment depends upon the age of the individual, the temperature 

 of the water, and the geographical locality. Bowerbank (1866, 



