OECELLA. 409 



pelvic bones are regarded as sacral, the vertebral formula of this genus is as follows : 

 C. 7, D. 12 or D. 13, L. 14 or L. 13, S. 2, C. 27 or 28 = 62 or 63. 



In an adult male O. fluminalis, with 13 vertebral ribs, in which the vertebral 

 segments had never been separated, these respective regions of the vertebral column 

 had the following measurements : C. 3"-90, D. 18"-80, L. 16"-80, S. 2"-50, and C. 25"-75 

 = 67""75, whilst in an adult gravid female of O. brevirostris with 12 ribs, but which 

 had had the intervertebral substance removed, the different portions of the column 

 were as follows : C. 3"-50, D. 14"-75, L. 16"-50, S. 2", and the caudal 26"-90 = 63"-65. 

 In the former of these specimens the total length of the skull was 12" and in the 

 latter ll"-75. 



Vertebral column. — The first two cervical vertebrae of this genus are the only two 

 segments which amalgamate with one another. Union takes place at an early age, 

 but the amalgamation of the neural arches is never complete, as they are partially 

 separated from each other by an incision which runs upwards for some distance from 

 the upper margin of the intervertebral foramen. This incision is also prolonged 

 downwards from the inferior border of the foramen, behind the posterior borders of 

 the facet for the occipital, and is partially prolonged outwards, to the base of the 

 transverse processes of the axis. The neural lamina of the 1st vertebra is broad 

 and strong, but that of the 2nd vertebra is feeble. The arch between the posterior 

 zygapophyses of the 2nd vertebra, as indicated by the incision, is of considerable 

 breadth as compared with those behind it. The combined arches of the 1st and 2nd 

 vertebrae send up a strong bifurcate spinous process, having behind it a short longi- 

 tudiaal ridge. The transverse process of the 1st vertebra is a large nodule du'ected 

 somewhat backwards and separated by a deep notch from the longer, more pointed, 

 and backwardly dnected transverse process of the axis. The antero-posterior length 

 of the bones inferiorly is about l"-25, whilst the longitudinal extension of all the 

 other cervicals together does not exceed 2"-25. The body of the 3rd vertebra has 

 an antero-posterior thickness of 0""35, but those behind it manifest a shght increase 

 to the 6th, whilst in the 7th there is a more marked thickening. 



The neural arches of the other cervical vertebrae are moderately high, and 

 highest and most peaked in the 3rd, 4th, and 6th, the arches of the 6th and 7th 

 being lower, but having more lateral expansioD The laminae are somewhat feeble, 

 and occasionally the lamina of one side does net unite with its feUow, and hence 

 there is only the feeblest trace of a spinous process. In the gravid female the 3rd 

 and 7th cervical and 1st dorsal present this feature. The superior transverse process 

 of the 3rd vertebra is well developed, dilated at its extremity and with a very slight 

 backward tendency. In the 4th cervical vertebra the process is much reduced in 

 size, and a forwardly bent inferior process appears, which is much more strongly 

 developed in the 5th, and is elevated in position on the 6th, in which it can be merely 

 traced. The upper transverse process is lost on the 5th vertebra, but on the 6th 

 segment a small upper transverse process appears, and in the 7th it is prominent 

 on the under surface of the bodies of the 4th and 5th vertebrae ; there are two nodular 

 hypapophyses and an azygos process on the 6th and 7th. Prom these facts it is evident 



d3 



