ORTHOCERAS LiEVIGATLM. 15 



(according to de Koninck) occupying about one-fourth of the total length of the 

 shell ; the last portion free from annulations. Septa numerous, slightly oblique, 

 occurring in the centre of the furrows between the annulations, very shallow. 

 Siphuncle small, subcentral. Ornaments consisting of regular, prominent, 

 rounded annulations, undulating as they encircle the shell, almost as strong upon 

 the cast as they are where the test is present. The latter is thin, and is covered 

 with regular transverse lines, somewhat less than 1 mm. apart, so that about 

 eight of them cover the space occupied by one of the annulations and the furrow 

 next to it. In a specimen measured there were in a length of 75 mm. eighteen 

 annulations, six of which occupy, at the narrower part of the shell, 25 mm. 



Affinities. — Orthoceras cyclophorum, Waagen,' from the "Productus Limestone" 

 of the Salt Range in India, resembles the present species very closely, so far as 

 the fragmentary specimens representing it w-ill allow of a comparison being made. 

 The two fragments consist only of three and four annulations respectively. The 

 septa are described as " somewhat oblique," the siphuncle excentric, " removed 

 from the centre a little more than its own thickness." The general aspect of the 

 two forms is strikingly similar, but until more complete examples of the Salt- 

 Range species are found it is no doubt wiser to keep the latter separate from the 

 European species. There is very little resemblance in either of them to Orthoceras 

 undatura of Fleming." The latter tapers rapidly (about 1:4); the annulations 

 are very numerous, being only 3 mm. apart where the diameter of the shell is from 

 12 to 20 mm., and they are at a very slightly varying distance from each other. 

 Orthoceras ohliqiie-annulatiirii, Waagen,' is a small fragment exhibiting five or six 

 oblique annulations. It may have been the younger portion of a shell, or, on the 

 other hand, a fragment of a small species. The siphuncle is described as central. 

 Its rate of tapering (about 1 : 18) greatly exceeds that of Orthoceras laevigatura, 

 though falling far short of that of 0. undatum. Gyrtoceras dactyliophorum, 

 de Kon.,* appears to be only a curved example of the present species ; the 

 siphuncle is small, cylindrical, and central, and therefore essentially different from 

 that of Cyrtoceras, in which it is large, marginal, and beaded. The curvature is 

 thus the only character which this species has in common with Cyrtoceras. 



Beraarhs. — This is a somewhat rare species. I have collected it at Clane and 

 St. Doulagh's, but the specimens figured, kindly lent to me for that purpose by 

 ^Ir. J. Nolan, of the Geological Survey of Ireland, are from Ardlaraan, in the 



1 ' Mem. Geo). Surr. India ;' ' Palaeontologia Indica,' ser. xiii ; Salt-Kange Fossils,' vol. i ; 

 ' Productus Limestone Fossilo,' 1887, p. 68, pi. vi, figs. 7, 8. 



2 ' Annals of Philoaoplij-,' vol. v, Jan. — June, 1813 (" Observations on tbe Orthoceratites of 

 Scotland "), p. 199, pi. xxxi, fig. 12. 



•'' 'Mem. Geol. Surv. India ;' ' Pal. Ind.,' ser. xiii, Salt-Range Fossils, vol. i ; 'Productus Lime- 

 stone Fossils,' 1887, p. C8, pi. vi, figs. 7, 8. 



* ' Calc. Carb. Belg.,' 1880, pt. 2, p. 30, pi. siiiv, fig. 1. 



