Prof. W. King 07i Spirifer cuspidatus. 17 



In the first stage in the process of inibbing down the umbone, 

 the section (PI. III. fig. 17), at the depth of one-eighth of an 

 inch, displayed the dental plates (a) and the septum (b) ; the 

 latter was nearly on a line with the area. In the second (fig. 18), 

 at the depth of a quarter of an inch, the septum was more clearly 

 distinguished as an independent structure; and its centre showed 

 a trace of the canal (c). In the third (fig. 19), half an inch in 

 depth, the septum was placed much further in, and the canal, 

 now more obvious, was situated in the centre of its back. In 

 the fourth (fig. 20), five-eighths of an inch, the canal, hitherto 

 filled with a shelly deposit, was well displayed, and exhibited 

 evidences of a foreign-mineral infilling. In the fifth (fig. 21), 

 three-quarters of an inch, the septum was somewhat reduced 

 in thickness, but the canal was larger and well filled with 

 adventitious matter. In the sixth (fig. 22) seven-eighths of 

 an inch, the septum had disappeared ; the canal, however, was 

 still present. In the seventh (fig. 23), one inch, the tube was 

 getting faint ; still the dental plates were seen crossing the 

 entire width of the umbonal cavity. In the eighth and final 

 stage, one inch and an eighth, both the canal and the central 

 portion of the dental plates were gone. 



It is thus evident that the septum and canal were an early 

 development — that the latter became gradually filled up with 

 a shelly substance in its oldest part, but remained open for 

 about three-eighths of an inch at its distal extremity — that the 

 canal projected beyond the free margin of the septum for about 

 a quarter of an inch, and terminated on a level with the centre 

 of the free margin of the dental plates. 



These points are exactly in accordance with the appearances 

 presented by a beautiful fossil cast, from the State of Ohio, for 

 the loan of which I feel much indebted to Mr. Davidson : in- 

 deed the resemblance is such as to strongly impress me with 

 the idea that the cast belongs to a shell specifically identical 

 with Martin's Spirifer cuspidatus. 



The canal of Spirifer distanSj according to Davidson's figure, 

 also remains open at its extremity ; and such is the case in the 

 Galway specimen of this species (fig. 10) ; it appears, however, 

 to be more incomplete, and to rise more from the back of the 

 septum, than the one belonging to Spirifer cuspidatus. 



Some additional investigations which I have recently made 

 among a number of other Spirifers may now be brought under 

 notice. As Spirifer striatus is the type of the genus*, I am 

 induced to give some details of its corresponding apophysis. 



* This has been shown to be the case by Mr. Davidson, in the Intro- 

 duction to his 'British Fossil Brachiopoda/ p. 81. 



Ann. & Mag. N. Hist. Ser. 4. Vol. ii. 2 



