Lyman.] 108 [March 7, 



be added, so as to represent a single line, it will be found that the 

 combined length in A. Agassizii is about one hundred and eighty-four 

 times the diameter of the disk; and in A. costosum about two hun- 

 dred and fifty-eight times. In other words, a specimen of A. costo- 

 sum, whose disk was less than one and one-half inches across, would 

 have an arm thirty feet long. 



Using the same unit, the arm of Ophiothrix longipeda — (the long- 

 est armed species among Ophiothrix) would measure only two feet 

 and three inches. 1 



Description of Plates. 



Plate 4. Astrophyton costosum Seba. Diagram of the right-hand stem (one-half 

 an arm) carried out to its last forks. Each shaft in this and the two succeeding 

 plates has been measured separately, and is drawn in proper proportion. The fig- 

 ures indicate the order of the forks as counted from the disk. 



Plate 5. Astrophyton Agassizii Stimpson. The same treatment as in Plate 4. 



Plate 6. Astrophyton asperum Agass. The same treatment, except that only the 

 right-hand branch, at fork two, is carried out to its ultimate forks. It was not pos- 

 sible to unroll and measure the mass of fine twigs which composed the rest of the 

 half arm. 



Plate 7. Diagrams of different forkings. Fig. 1. A young A. Agassizii, from 

 nature. Fig. 2. Type of A. costosum. Fig. 3. Type of A. Agassizii. Fig. 4. Type 

 of A. asperum. Fig. 5. Forking of the club-moss Selaginella. Fig. 6. Type of 

 regular dichotomy. 



The Librarian announced the gift of a large number of 

 valuable books, chiefly botanical, from ,the Hon. Oeorge B. 

 Emerson, to whom the thanks of the Society were voted. 



1 Since writing the above, I have had the opportunity of examining the arms of 

 A. verrucosum, on which Agassiz wrote his valuable monograph. (Sur quelques 

 points de l'organisation des Euryales. Mem. de la Soc. Sc. Nat. Neuchatel, n, 

 1839.) The disk was 80 mm. in diameter. Starting at fork two of the right branch, 

 the left stem is remarkable for poverty of twigs ; the right for abundance. Thus 

 the twig at fork thirteen of the left stem has but three forks ; that of fork thirteen 

 of the right stem has about three hundred. The whole number of forkings from 

 the main (right) stem is thirty-five; and some of the outer twigs (e. g., at fork thir- 

 teen) have more forks than the inner (e.g., at fork five). Agassiz's plate was drawn 

 from a small, dry specimen, and the finer twigs could not be represented in detail. 



