100 HORN EXPEDITION — PALAEONTOLOGY. 



Loc. — In limestone, north of Teinpe Vale, Laurie's Creek, Middle Valley at 

 Tempe Downs. 



Opthocepas larapintense, sp. nov. (Plate I., Fig. 3.) 



Sp. char. — Shell elongate, straight ; rate of increase one in ten ; section 

 circular. Septa rather deeply concave, sutures slightly Insinuate ; the distance 

 between the sutures is about one-tenth the diameter. Siphuncle central, about 

 2 mm. in diameter. The species is founded on a single specimen, which shows 

 three septal chambers in a length of 8 mm., succeeded by a cylindroid body- 

 chamber 78 mm. long, and 20 mm. and 28 mm. diameters at the proximal and 

 distal ends respectively. The subtending apical angle indicates a shell of about 

 nine inches in length. 



Obs. — O. larapi}itense approximates to O. gossei, from the same beds, in its 

 narrow septal chambers ; but in that species the siphuncle is lateral in position. 

 It resembles also O. perversum, Blake, in its narrow septal chambers ; but that 

 species has an unsym metrically placed siphuncle, an elliptic section, and the shell 

 does not taper so rapidly. 



Loc. — In limestone, Tempe Downs. 



Orthocepas chewingsi, sp. nov. (Plate I., Fig. 1.) 



Sp. char. — -Shell elongate, straight, rate of increase one in nine, section 

 circular. Septa distant about one-third the diameter, moderately concave, sutures 

 direct. Sii)huncle central, about 1'5 mm., where the shell has a diameter of 

 12 nun. Test and body-chamber unknown. This species is based upon two 

 specimens, the larger of which is a fragment 80 mm. long and 27 mm. diameter at 

 the distal end ; it is without septa and siphuncle, though the sutural lines (ten in 

 number) are distinct. The other specimen is nearly complete, except the body- 

 chamber, and measures 80 mm. long ; the septa and siphuncle are present. The 

 two specimens I regard as conspecific, because the rate of increase of the shell and 

 the sutural distances are the same. 



Obs. — This species agrees with O. kittneknllense, Foord, " Cat. Foss. Ceph., 

 Brit. Mus.," p. 2, fig. 1, of the Swedish Ordovician in its circular section and 

 sutural distances, l)eing about the widest known, but it differs fi'om it by its 

 central siphuncle. Orthoceras, sp. ind., t. 4., f. 9, in Johnston's Geol. Tasm., may 

 possibly belong here. 



Loc. — In limestone, Laurie's Creek, Petermann Creek, and Tempe Downs. 



