SOLENOCHEILUS CLAUSUS. 207 



and outer whorls; they are 6 mm. apart where the sides of the shell have a breadth 

 of 16 mm., and 8 mm. apart where the latter has increased to 21 mm. The prin- 

 cipal dimensions of the shell are as follows: — Diameter 115 mm., height of outer 

 whorl near the aperture 35 mm., breadth of peripheral area at the same place 

 55 mm., breadth of umbilicus 57 mm., diameter of its central vacuity 1 1 mm. The 

 test bears no trace of ornamentation except in the first whorl, where fine and rather 

 distant longitudinal ridges are developed. 



Genus Solenocheilus (see ante, p. 126). 

 Solenocheilus clausus (see ante, p. 130). 



When describing this species only one specimen was available, and as the 

 siphuncle was not to be seen in it I felt doubtful as to its belonging to Solenocheilus. 

 This doubt is removed by the information supplied by a small specimen that lately 

 passed through my hands in which the position of the siphuncle is characteristically 

 peripheral. This specimen is from the same locality, Little Island, near Cork, as 

 the original one. A large crushed and distorted specimen from this locality in Mr. 

 James Duffy's collection measures 223 mm. in the longer diameter of the ellipse into 

 which it has been drawn out. It has a deep and wide hyponomic sinus in the 

 aperture. 



Remarks. — During the preparation of this part of the present Monograph I have 

 been favoured by Dr. E. von Mo j si so vies with a copy of the supplementary part of 

 his valuable memoir on the Cephalopoda of the Hallstatter Kalke (in ' Das Gebirge 

 um Hallstat,' Abtheilung 1, Band i, Supplement Heft, Wien, 1902). The oppor- 

 tunity is thus afforded me of referring to it in connection with the genus forming the 

 subject of this addendum. 



In the " Phylogeny of an Acquired Characteristic" (extr. from 'Proc. Amer. Phil. 

 Soc.,' vol. xxxii, No. 143, Aug. 20, 1894) Professor Hyatt established the genus 

 Si/n'iujoceras for the group of Nautilus Barrandei, E. v. Mojs., to include " Triassic 

 species like the type, Si/ruKjun.'rax <j ra it tdosustrit it 'tis , which have a tubular, nepionic 

 volution with the siphuncle subventran [marginal as to the periphery]. The early 

 nepionic [immediately post-embryonic] shell is also ornamented with very elosely 

 set transverse ridges, but it has no longitudinal ridges until a comparatively late 

 stage. This nepionic ornamentation is like that of the genus Hercoceras at the same 

 age. The impressed /one is present only after contact, and is not deep." 



Dr. von Mojsisovics accepts this genus (p. 214 of his work above quoted), but 

 includes in his synonymy of it " Solenocheilus (Meek and Worthen), Foord" (' Cat. 

 Foss. Ceph. Brit. Mus.,' pt. 2, p. 165), without any reference to Hyatt's amended 

 diagnosis of Suleiiuclwilu.i in the 'Geological Survey of Texas' ("Carboniferous Cepha- 



