74 PROCEEDINGS OF THE NATIONAL, MUSEUM, vol.61. 



The longitudinal section is quite original. Each pinnule is formed 

 of two bundles, one coming from the right and the other from the 

 left of the zoarial axis. The tubes are cylindrical ; they are separated 

 by a very large interzooecial canal. 



The interpretation of the sections causes us to suppose that the 

 reunion of the pinnules on the median axis of the zoarium arises 

 from the reunion of two lateral and symmetrical pinnules of Trmi- 

 catula. In reality the form Unicytis precedes the form Truncatula 

 for it exists at the extremity of branches of specimens of this latter 

 genus. It is more correct to say that Truncatula is derived from 

 Unicytis by the separation of the two bundles forming each pinnule 

 of the latter genus. We may add that the different forms of the tubes 

 in these two genera imply some anatomical differences necessitating 

 their separation. 



Occun^ence. — Cretaceous (Santonian) : Vendome (Loir-et-Cher), 

 France. 



riesiotype.—Csinu collection and Cat. No. 68993, U.S.N.M. 



Genus SEMICYTIS D'Orbigny, 1854. 



1854. Semicytis d'Okbigny, Paleoutologie fraugaise, Terrain Cretace, vol. 

 5, p. 1048. 



The ovicell is placed on the cellular face, in the vicinity of the 

 pinnules. The tubes are subcylindrical, oriented, little expanded, 

 without peristome, with dorsal gemmation axial and irregular. No 

 basal lamella. The apertures are placed on the anterior face of the 

 trunk and of the pinnules. The mesopores are more or less numerous 

 between the apertures. The zoarial dorsal is formed of a very large 

 lamellar epitheca perforated by rectilinear vacuoles. 



Genotype. — Semicytis disparilis D'Orbigny, 1854. Turonian-San- 

 tonian. 



Structure. — As in the other genera of the same family, the gemma- 

 tion is not exactly dorsal; it does not occur on the basal lamella. 

 There are rather successive ramifications on a variable plane in the 

 vicinity of the zoarial axis; the ramified tubes are sometimes poly- 

 pidian and are then oriented towards the anterior face, sometimes 

 aborted and oriented towards the posterior where they perforate a 

 very thick epitheca of lamellar tissue. 



This genus differs from Ti-ancatuJa Hagenow, 1851, in the pres- 

 ence of mesopores. Its characteristics have been well recognized by 

 D'Orbigny. Gregory reunites it with Homoeosolen but it differs, 

 however, in the presence of adventitious tubes, vacuoles, and meso- 

 pores. It differs from Desmepora Lonsdale, 1850, in the presence of 

 a lamellar tissue, which is dorsal and not peripheral, in the absence 

 or great reduction of the zone of nematopores, in the presence of 



