402 PROCEEDINGS OF THE AMERICAN ACADEMY 



of. anterior transverse, or annular furrow, a/i. dorsal part of a/. 

 ■pf. posterior transverse, or annular furrow. 

 mf. median, or longitudinal furrow. 

 d. depression on the ventral side. 

 cv. contractile vesicle. 

 m. mouth, m^. anterior edge of m. 

 <E. oesophagus. 

 do. digestive vacuoles. 

 fl. pseudo-flagellum. fi^. base of ,^. 



n. nucleus, or generative organ, ne. envelope of n. This is the reproductive 

 organ, properly speaking, and n is the contents, or reproductive material, the future 



eggs- 



t. nucleolus, or testes. 



■pc. pseudo-cuirass. 



I., 11. The two products of self-division. III. The annular constriction which 

 finally separates I. and II. 



Figs. I to 7. Peridinium Cypripedium, n. sp. 



Fig. 1. Profile of an adult, seen from the left side. Mag. 500 diam. 



Fig. 2. View of the ventral side of an adult. Mag. 500 diam. 



Fig. 3. Posterior view of an adult; the anterior end in the distance. Mag. 500 

 diam. 



Fig. 4. A young individual. Mag. 300 diam. 



Fi"-. 5. An adult gradually dried up. Dorsal view, to show the arrangement of 

 the punctiform ornamentation of the derm. 500 diam. 



Fi"'. 6. The process of self-division, just half an hour before separation. Ven- 

 tral view. 200 diam. 



Fig. 7. Profile of I. fig- 6, just at the moment of separation. 200 diam. 



The following memoir by Mr. Francis was presented by 

 Professor Treadwell with these introductory remarks ; — 



About five years ago I called the attention of the Academy to the 

 subject of the strength of cast-iron columns, and presented a paper, 

 which was printed in the Proceedings, containing a short examination 

 of the state of our knowledge upon that subject. It was then thought 

 desirable that a more elaborate examination should be given to it ; and 

 a committee was appointed for the purpose. This committee, after 

 two or three consultations, gave over all attention to it, and there the 

 matter has rested, so far as the committee, as a body, were concerned, 

 to this day. One of their members, however, Mr. J. B. Francis of 

 Lowell, whose professional engagements gave him a particular interest 

 in the investigation, finding that nothing would be done by the com- 

 mittee collectively, took up the subject in his own way, and has pur- 

 sued it at his leisure up to the present time. lie has made a most 



