30 JOHN M. CLARKE 



RELATIVE ABUNDANCE OF LIVING AND DEVONIAN SPECIES 



Continuing to use the ''Challenger" reports we find a contrast in 

 the abundance of individuals growing in any one place, but in 

 making this comparison we must remember that the zoologist is 

 dipping into the sea bottom with a rake on the end of a string, 

 while the paleontologist is on the sea bottom itself, with dynamite, 

 crowbar, and hammer. The "Challenger's" dredgings rarely found 

 any considerable number of individuals at any one place; "gen- 

 erally only one or two specimens of each species were obtained 

 at the same locality. Sometimes, however, a considerable number 

 of specimens were found at once." None of this evidence seems 

 to point toward colonies or plantations in such vast numbers as in 

 the Devonian. Today the strongholds of the hexactinellids are 

 about the Philippines, Little Ki and Kermadoc islands; in the 

 deeps of the southern Indian Ocean between Prince Edward and 

 Crozet islands; and in Atlantic waters, off the Bermudas and 

 St. Thomas. 



ONTOGENY OE THE DEVONIAN SPONGES AS AN INDEX OP THEIR 

 ADVANCED AGE AND SPECIALIZATION 



There are four simple types of morphology, contemporaneous 

 and combined, among the Devonian dictyosponges : (i) the smooth 

 obcone, regularly expanding like a cornucopia and gently con- 

 tracting about the open aperture; (2) a six-sided prismatic or 

 banana shape; (3) a subprismatic obcone with successive trans- 

 verse rows of tufted nodes, typically eight to a row ; (4) long obcones 

 with conxntric rings, like the horn of an Oryx. These simple 

 expressions have a successive value in ontogeny. 



The first group constitutes the genus Dictyospongia. The 

 second, in its typical expression, is the genus Prismodictya; but 

 in several species not included in that genus the prismatic phase is 

 superinduced upon and subsequent to the smooth phase. In other 

 genera or species the later growth of the prism may show a tendency 

 to develop nodes at the prism angles. Hydnoceras is the name 

 applied to the typical tuberous or nodose forms and Ceratodictya 

 expresses the annulated phase. These different expressions are, 

 as just observed, essentially successive in the chronologic order of 



