200 Association of Geologists and JYaturalists. [Nov., 



is a tendency to a pentangular form, the largest tentacle being on 

 a line with the long diameter of the mouth. The Actinia, at 

 least, is bilateral or symmetrical, and this is probably a universal 

 law. They are very variable in their form at different times. 

 They are divided into as many lamellae as there are tentacles; 

 these lamellae are muscular membranes, going from the top to the 

 centre, tor the movements of the animal; the tentacles have both 

 longitudinal and circular fibres. The same animal is both ovipa- 

 rous and vivaparous — the digestive cavity, widely open below, 

 receives the food always mixed with water — the tentacles are 

 folds from the body of the animal. 



In the Tubulariae, the ovaries hang outside the body, between 

 the tentacles. There is the closest affinity between the common 

 Polypi and the Actiniae; they also vary much in form, and have 

 both vertical and circular muscular fibres. The affinities between 

 all the radiated animals are very striking; for instance, the Echi- 

 narachnius seems to be different from the Medusae, only in having 

 a hard shell. 



Prof. Dana confirmed these views of the bilateral character of 

 the Radiata, by his observations on Madrepores; in the Zoan- 

 thidae, one tentacle is larger than the rest, and white, while the 

 rest are green. He did not find the tentacles, a multiple of the 

 number five in the corals, but rather of four. In the Actinia of 

 Boston harbor, the lamellae are arranged in couplets. 



Prof. Agassiz believed the tentacles of the Actinia were mul- 

 tiples of five — even in the corals, he was glad to see that Prof. 

 Dana found that the mere fact of their tentacles being a multiple 

 of four, was not an objection to their bilateral structure; even in 

 them this idea is still more confirmed. In the Lucernaris, there 

 are colored oculiform spots, the beginning of eyes; hence there 

 must be a nervous structure. 



The evening was spent most delightfully at the house of Hon. 

 Abbott Lawrence, where the members received a most cordial 

 welcome. 



Morning Session — Thursday, Sept. 23. 

 On the Mastodon, by Dr. J. C. Warren. 



The first notice of this animal, seems to have been in the first 

 part of the last century. Mr. Jefferson made a collection of these 

 bones, which was sent to Paris, and examined by Cuvier. 



A mastodon was found a few years ago, in New Jersey, which 

 is now at Harvard University. In 1845, one was found at New- 

 burgh, which belongs to Dr. Warren. Four out of five skeletons 

 were found in or near New York state. 



The mastodon and elephant belong to the same order; and the 

 different resemblances and differences were clearly pointed out. 



