O. C. Crick — On Nautilus robust us. 345 



distance of the periphery from the preceding whorl 42 mm., the 

 centre of the siphuncle is 13-5 mm. from the preceding whorl, and 

 therefore 28*5 mm. from the periphery. The position of the siphuncle 

 may therefore be described as infra-median, or, in the terminology 

 suggested by Professor Hyatt,^ ' intracentrodorsan.' 



The other French specimen originally referred to this species, 

 viz., the example in the British Museum bearing the register 

 number 37,005, also belonged to the Tesson Collection, and bears 

 an original label with the following inscription : " \_Naut]ilus 

 inornatus, d'Orbigny. [Lias] sup[eriieur. Curcy." It has the 

 following measurements: diameter (without test near aperture), 

 166 mm. ; thickness (without test on one side), 116 mm. ; width of 

 umbilicus (with test), 25 mm. These dimensions agree very closely 

 with those of the type-specimen, the latter having the following 

 dimensions at a diameterof 160 mm. : diameter (with test), 160 mm. ; 

 thickness, estimated at about 117mm. ;'^ width of umbilicus (with 

 test) , 26 mm. Only a small portion of the body-chamber is preserved. 

 So far, then, as external characters are concerned, it does not seem 

 possible to separate this example from the type-specimen o^N. robustus. 

 It is true that the example from Curcy is labelled " Lias superieur," 

 but since the Middle Lias, including beds corresponding to our 

 Marlstone, also occurs at the same locality,^ it is quite possible that 

 the specimen may have come from these beds. 



Of the examples belonging to the Cheltenham College Museum 

 that we refer to this species, the larger one is stated to be from the 

 " Marlstone. Loc : unknown ; but probably near Cheltenham, and 

 possibly Alderton Hill." The measurements are : diameter of 

 shell (without test), 220 mm.; thickness (without test), 153 mm.; 

 and width of umbilicus* (without test), about 33 mm. ; from which 

 it will be seen that this example is not only somewhat larger than 

 the type-specimen, but it is also relatively somewhat thicker, 

 whilst the umbilicus is relatively somewhat narrower. The smaller 

 specimen is labelled "Marlstone, Gretton," [near Dumbleton]. It 

 has the following dimensions : diameter (without test), 165 mm. ; 

 thickness (without test), 119 mm. ; and width of umbilicus (with 

 test on one side), 26 mm. Only a small portion of the body-chamber 

 is preserved. These dimensions agree fairly well with those of 

 the type-specimen at a diameter of 160 mm. Also the general 

 characters of these fossils agree so well with those of the type, 

 that it will probably be correct to regard the slight differences in 

 their dimensions as merely individual variations. 



It may be useful to give in tabular form the measurements of the 



1 A. Hyatt, " Phylogeny of an acquired characteristic" : Proc. Amer. Philos. 

 Soc, vol. xxxii, no. 143 (August, 1894), p. 430. 



^ One side of the fossil is broken away, so that the thickness can only be estimated. 



2 " Le type normal du Toarcien de Normandie se trouve aus environs d'Evrecy, de 

 la Caine etde Cui-cy, ou la zone a Am. spinatus supporte une argile dite a Lepteena, 

 c'est-a-dire a petits brachiopodes d' aspect paleozoique, Koninckella, Cadomella, etc." 

 (Lapparent, Traite de Geologic, 4«'e ed., 1900, torn. 2, p. 1089.) 



^ The umbilicus is filled with matrix. 



