No. 560] 



6.1 .1/ B HI A X IIOLO Til CHI A AN 



503 



normal conditions, in the deep sea, in highly saline, alka- 

 line or acid water, in the regions of excessive cold or ex- 

 cessive heat (such as hot lakes), in stagnant pools in the 

 ocean bed, in brackish underground lakes or streams, or 

 in comparable situations; but apparently none of these 

 groups were highly adaptable; though very abundant, 

 they flourished through comparatively small extremes 

 in their physical and chemical environment, from which 

 subsequent vigorous types with the same or a greater 

 economic radius promptly ousted them. 



The disappearance of a group in a given horizon, it 

 should be pointed out, does not at all mean that the group 

 really vanished at that time; it means merely that at 

 that time it disappeared from the littoral. Most groups 

 undoubtedly persisted long after they ceased to occupy 

 a habitat which is now a geological stratum, under locally 

 unfavorable conditions, finally dying out at a time long 

 subsequent to the last record in the rocks. 



Not only does the deep-water habitat of the Klpidiida? 

 betoken a very ancient origin, but the group to-day is evi- 

 dently senescent. The extraordinary shapes assumed In- 

 most of the species can only be interpreted as a result 

 of an explosion of the characters induced by extreme 

 age. 



Thus, reasoning backward from a study of the recent 

 fauna alone, we should expect to find the Elpidiida? and 

 Artemia, or very closely allied forms, in the early paleo- 

 zoic rocks, representing the littoral in the age when 

 they were at the height of their ascendancy, and we 

 should be greatly surprised should they appear in any 

 post-paleozoic formation. 



Lorenzinia—Lorenzinia, mentioned by Dr. Clark, is 

 undoubtedly the cast of part of a medusa, as any one 

 acquainted with the literature on the fossil medusae can 



Mackenzie*. — The two specimens assigned to the genus 

 Macloizia appear to me to be undoubtedly mud-living 

 actinians of the family Edwardsiidae, closely related to 



