364 Prof. Allman on the Morphology 



the Silurian seas. Moreover the family Poritidce, which now 

 includes many of the most important of reef-building corals, 

 was also, even in palaeozoic ages, a family rich in reef-forming 

 species ; for some of the species of Favosites grew into hemi- 

 spherical masses eight or ten feet in diameter. It also seems 

 probable that the genus Alveopora has existed through all 

 periods from the paleeozoic to the present time, which would 

 seem the more remarkable considering the extreme delicacy 

 and fragility of these corals, and also the fact that, so far as 

 known, they are all shallow-water and reef species. 



XXXVIII. — On the Morphology and Affinities of Graptolites. 

 By Prof. Allman, F.R.S., F.L.S., &c.* 



Among the extinct forms of life few possess more interest than 

 these remarkable fossils, absolutely confined, as they are, to 

 one great section of the palseozoic rocks, where their vast 

 abundance, wide geographical distribution, and easy recogni- 

 tion render them of special value to the practical geologist. 



The Graptolites are now by most paleeontologists referred to 

 the Hydroida : and their living representatives are sought for 

 among the calyptoblastic genera of this order. "While, how- 

 ever, I am unable to recognize their hydroid relations from 

 the point of view from which pala?ontologists have generally 

 agreed to regard them, I believe that their affinities with the 

 Hydroida are too decided to justify their omission from any 

 complete exposition of the palseontological history of this group 

 of the animal kingdom. 



The typical form of a graptolite is that of a narrow tube, 

 straight or more or less curved, emitting from one side a series 

 of hollow denticles, which are the free extremities of little 

 cups or calicles, through which the cavity of the tube opens 



* Tlie following paper is mainly a portion of a chapter on the Distribution 

 of the Hydroida in Time contained in the second part of the author's 

 ' Monograph of the Gymnoblastic Hydroids ' now neai'ly ready for delivery; 

 and as it contains some new views of a question much agitated at this mo- 

 ment, it was thought that its regular publication might be here antici- 

 pated. The section of the work to which it properly belongs was printed 

 oft' some time ago, and consequently before the appearance of Dr. Nichol- 

 son's ' Monogi'aph of the British Graptolitidte,' the first part of which, 

 just published, will be welcomed by the palfeontologist as a very valuable 

 introduction to the systematic study of the graptolites. This difference 

 of date will explain the absence of reference to Dr. Nicholson's work in 

 the Monograph of the Gymuoblastea. Dr. Nicholson, however, does not 

 seem to have essentially modified the views contained in his earlier publi- 

 cations and discussed in that Monograph. 



