584 NEW YORK STATE MUSEUM 



the same manner as the formation of the funicle oy the sicula, viz by 

 the successive budding of two thecae, the second of which 

 buds from the first, and both of which, assuming 

 diverging directions, determine the direction of the 

 ranches. This shows that the sicula, with its distal part, holds 

 the position of a first theca, and that the funicle is genetically 

 and morphologically not different from the branches of a higher 

 order. From growth stages of Dichograptus and Loganograp- 

 tus, obtained in the Deep kill collection, it can be deduced that 

 the dichotomous branching of these genera conforms to the 

 same law. The hydrosome of a new species of Bryograptus, 

 common in the Tetragraptus beds, possesses the same mode of 

 branching. 



Holm 1 has demonstrated that in Didymograptus, Tetragraptus 

 and Phyllograptus the same mode of branching persists. 



As to the nature of the branching which has been termed 

 " monopodial " or " lateral," and which is characterized by the 

 continued growth of the original branch in the same direction 

 after division, I have been unable as yet to obtain any con- 

 clusive facts. The genera which show this mode of branching 

 most typically, are Schizograptus, Trochograptus, Holograptus 

 and Eouvilligraptus. The fact, however, that both dichotom- 

 ous and monopodial branching coexist in the hydrosomes of 

 these genera, seems to indicate, that there can be no funda- 

 mental difference between them. Observations on Coenograp- 

 tus (fig. 13) indicate the correctness of the suggestion of Wiman 2 

 that this mode of branching is produced by the greater strength 

 which is attained by the mother theca before it produces the 

 daughter theca, and which enables the former to retain its 

 jriginal direction while it compels the latter to a change of 

 direction. 



4 There must have existed physiologic and morphologic 

 differences between the zooids of the biserially arranged 



1 Sveriges Geologiska Undersokn. Afhandl. ocli uppsatser. 1895. ser. (X 

 no. 150. 

 2 Geol. inst. Upsala. Bui. 1895. no. 4, v. 2, pt 2, p. 34. 



