SrPPLEMEXT. 
385 
Ascoceras. Dr. Lindstrom, having lately completed his researches 
in this and kindred genera, has embodied them in a richly illus- 
trated memoir written in English, and entitled “ The Ascoceratidse 
and the Lituitidse of the Upper Silurian Eormation of Gotland.” 
This was communicated to the Eoyal Swedish Academy of Sciences 
11th Dec. 1889, and was published in the Proceedings of that 
institution for 1890. Most of the observations and descriptions 
which follow are given in Dr. Lindstrom’s words, only a few 
passages, not deemed to be of primary importance, being omitted. 
Dr. Lindstrom divides the family Ascoceratidce into four genera — 
Ascoceras, Barrande ^ ; Glossoceras, Barr. ^ ; BiUingsites, Hyatt ^ ; 
and Choanoceras, gen. nov. 
The common feature in their structure, that unites all these 
genera, is the abnormal growth and morphology of the septa 
formed during the last stage of their existence. Having begun 
with regularly formed septa, the later ones are bent obliquely in a 
sort of high saddle towards one of the sides (fig. 84, A), and all that 
succeed the first sigmoid septum are incomplete or leave a large 
lacuna in their central part (fig. 84, C, D), which lacuna is framed 
by the lateral borders of the septa. The siphuncle is broad, with 
nummuloidal or bulbous elements. The first three genera have 
attained a more pronounced development of the characteristic 
structure, which has been coming on by degrees in Choanoceras, 
without such a sudden transition from a Xautiloid stage as in them. 
A common feature in them all is the truncation, which seems to 
have been repeated several times. 
The systematic position and the afiinities of this family have long 
been a puzzle, at least, as long as the last stage of growth was the 
only one known. As Barrande left this group, it consisted of the 
two genera Ascoceras and Glossoceras, he himseK having declared 
that Apliragmites could not any longer be retained as a distinct 
genus, and that both its species coincided with true Ascoceras forms. 
^ Kongl. Syenska Tetenskaps-Akademiens Handlingar, Bandet 23, No. 12, 
Stockholm, 1890. 
^ Oesterr. Blatt. fiir Litt. u. Kunst, 1847 ; Haidinger’s Berichte iiber d. 
Mittheil. v. Freund, d. Naturwiss. in Mien, 1847, p. 268; also Bull. Soc. Geol. 
France, 1855, ser. ii. vol. xii. p. 157. 
^ Syst. Sil. de la Boheme, 1867, vol. ii. pt. i. p. 372. 
^ “ Genera of Fossil Cephalopods,” Proceed. Boston Soc. Nat. Hist. vol. xxii. 
1883, p. 278. BiUingsites is a Silurian genus closely allied to Ascoceras. The 
type species is Asc. Canadense, Billings, Eep. Prog. Geol. Surv. Canada, 1853- 
56, p. 310. 
PART n. 2c 
