150 Dr. A. H. Foord — AcantJionatitilus, Carhoniferous Limestone. 



of one spine to the base of the other, is 13-5 cm. The distance 

 between the septa, measured from the posterior to the anterior, is 

 14 mm., 17 mm., 20 mm., 13 mm., and 12 mm. 



Remarks. — The presence of the long, marginal spines dissociates 

 this form from any other Nautiloid shell known to me, and dictates 

 its generic appellation, while it also constitutes its chief specific 

 character. 



In seeking for species related to the present one in their general 

 form, those comprised under the genus SolenocheUus (Meek and 

 Worthen), and its congeners LopJwceras (Hyatt) and Asymptoceras 

 (Ryckholt, emend. Hyatt), suggest themselves as being the nearest 

 to it. In some of these species there arise from the angles of the 

 margin of the aperture spout-like projections which at first sight 

 might be taken, in their imperfect condition, for the stumps of spines 

 similar to those of the present species. Such appendages are seen 

 in a species described by Meek and Worthen ^ under the name of 

 Nautilus (SolenocheUus) Leidyi (Lophoceras Leidyi of Hyatt).^ This 

 species (which was found in the Keokuk beds at Warsaw, Illinois), 

 consisting only of the body-chamber, has on each side of the shell, at 

 the junction of the lateral margin and the umbilical wall, a " kind of 

 pinched prominence," which " seems even to have projected outward 

 somewhat as in Argonauta gondola of Adams,^ though probably not 

 to the same extent." It is clear that the spout-like projections here 

 described correspond in no waj', except in their position, with the 

 long, flat spines of AcantJionautilus bispinosiis. The former may, like 

 the hyponomic sinus of the aperture, have given exit to some of the 

 tentacular appendages ; the latter, not being channelled, could have 

 served no such purpose. What purpose they did serve it is difficult 

 to conceive, but it is safe to say that they furnished, in a measure, 

 a safeguai'd against attack. 



The thickened rim of the umbilicus is paralleled only in one other 

 Nautiloid, so far as I know, viz. the Nautilus ierebratus of Dumortier* 

 from the Upper Lias of La Verpilliere (Isere), France, and of 

 Lincoln. The rim of the umbilicus in this species ends in a slightly 

 prominent lateral angle. 



As the spines in the present species are perfectly symmetrical, it 

 is obvious that they were secreted by symmetrical organs. What 

 these organs were, must be matter of pure conjecture. It cannot be 

 supposed that they were of the nature of the tentacles of the Nautilus 

 or of any of the cuttle-fish tribe now existing. There is reason to 

 suppose, however, from their hollow structure that the spines were 

 secreted from the inside. 



^ Geol. Surv. Illinois, V, Geol. and Palseont, 1873, p. 521, pi. xviii, figs. 2, 2a. 



' Geol. Surv. Texas, Fourth Annual Report, 1892 (1893-) — Carboniferous 

 Cephalopods (second paper), p. 466. 



^ For a figure of this see Lovell Reeve in Conch. Iconica, vol. xii, 1860, pi. iv, 

 fig. 3. I have not access to the original source of the species. 



* Etudes Paleontologiques sur les Depots Jurassiques du Bassin du Rhone, pt. iv 

 (Lias Superieur) ; see also Catalogue of Fossil Cephalopoda in the British Museum, 

 pt. ii, 1891, p. 204, £. 36, 37. 



