crick: O-N AJfPnOBEOPSIS PAUCICA.VEh'ATA. 135 



about 10 mm. wide and rather more than 1mm. deep, -which seems 

 to have been continuous around the body-chamber, but owing partly 

 to the imperfection of the dorsal surface of this part of the body- 

 chamber, and partly to the presence of test there, its direction on the 

 dorsal area cannot be traced; it crosses the cast almost horizontally 

 on the lateral area, its centre being about 31 mm. from the edge of 

 the aperture ; it then rises in a broad obtuse V-shaped curve on the 

 dorsal surface, its centre in the middle of this surface, where it is 

 a little shallower than elsewhere, being 26 mm. below the edge of 

 the aperture. This depression was due to a corresponding thickening 

 of the internal surface of the shell. The septate part is very short, 

 only about 1 7 mm. long or about one-fifth of the length of the body- 

 chamber ; the test is present only on one lateral area and the adjoining 

 portion of the dorsal surface, and is continued over the posterior septal 

 surface ; apparently there ai-e only two camerse ; the septa are oblique, 

 nearly horizontal in the siphuncular region and strongly arched upwards 

 in the ventral region, so that the suture-lines are nearly straight on 

 the sides, form a broad, very shallow, backwardly-directed curve on 

 the dorsal surface, and a broad, forwardly-convex curve on the ventral 

 area. The internal cast of the last chamber is well-preserved, and 

 shows that its depth at the flattened dorsal surface of the fossil is 4 mm. 

 The dorsal portion of the internal cast of the penultimate chamber is 

 broken, and shows (beneath the ridge marked s' in the figures) a portion 

 of the posterior surface of the internal cast of the last chamber ; one 

 side and a piece of the adjoining dorsal area of the posterior surface 

 of the internal cast of the penultimate chamber are covered by the 

 test continuous with that on the sides, the rest of the posterior surface 

 is devoid of test ; the test is so fractured that it now only partly covers 

 the siphuncle, but it appears originally to have completely covered this 

 structure ; it is slightly thicker here than on the body-chamber, but 

 seems, like the rest of the test, to be quite smooth. The siphuncle 

 [si in Figs. 2 and 3) seems to be moniliform; it is subcentral, being 

 situated on the shorter (ventre- dorsal) diameter, a little nearer the 

 dorsal than the ventral surface. Parallel to, and at a distance of 

 7 mm. from, the edge of the penultimate septum, the test on the 

 lateral area and the adjacent dorsal surface is traversed by a feeble 

 depression bounded anteriorly by a well-defined, slightly-elevated 

 shoulder (r) ; the depression is continued as a very shallow groove (g) 

 over the posterior surface of the internal cast of the penultimate 

 chamber to a small fragment of the test on the opposite lateral area 

 (see Fig. 2), which also exhibits a feeble depression bounded anteriorly 

 by a slightly-elevated shoulder (r in Fig. 2), The appearance of the 

 posterior part of the specimen shows that, like some other Nautiloids,' 

 this species was in the habit of discarding its earlier chambers and 

 covering the posterior septal surface with shelly matter ; the 

 slight shoulder, just mentioned, indicating the position of the edge 

 of the septum immediately behind which the earlier chambers were 



E.g. Orthoceras trimcatum, Barrande, from the Silurian of Bohemia and England, 



