OGYGIA. 



177 



ASAPHID^ — continued: Ogygia, &c. 



As must sometimes happen, in writing a continuous monograph, new materials, 

 connected with plates and descriptions already completed, turn up just as the work has 

 passed through the press ; and if such material refer to plates long since issued, it would 

 be of course desirable to leave the new matter to the end of the work ; but if not too 

 far removed, it is as well to insert it as nearly as possible in its place. 



Before proceeding, therefore, to the description of Illtsnus, to which group the present 

 part of the Monograph is restricted, we give a plate (numbered PI. XXV*) of Ogygia 

 peltata, containing the new and more perfect specimens to which reference has been made 

 in the "Corrigenda" of the volume for 1864. A new species has also occurred in the 

 same locality, and from the same formation (the Arenig or Skiddaw Rock, a set of beds 

 but little known). I had better describe the two forms of Ogygia together; I take also 

 the opportunity of inserting a new Barrandia at the same time. 



Ogygia peltata, Salter (PI. XVII, figs. 8—10). PI. XXV*, figs. 1—4. 



In page 133, line 1, it was stated that on PL XVII, figs. 9 and 10 are wrongly 

 marked as 0. peltata; and in page 134, our fig. 10 was described as 0. scutatrix, a 

 species which is only yet known from the Tremadoc llocks. 



The mistake arose, as stated in the Corrigenda, from laying too much stress on the 

 broad form and broad axis of the female form {'forme large of Barrande), which in Ogygia 

 peltata resemble those of 0. scutatrix : and, following the same idea, the head of the 

 broad form, with its wide labrum, was also described as 0. scutatrix (p. 133, line 22, &c.). 



These mistakes are now rectified by the accompanying plate (PI. XXV*), which 

 exhibits fine specimens of the broad form (figs. 2, 4) ; the shape of the head, with its 

 oblong parallel-sided glabella, in fig. 1 ; and the labrum, of full size (fig. 3). The eyes, it 

 will be observed, approach the glabella closely, as in PI. XVII, fig. 10, and are not placed 

 wide apart, as in fig. 8 of that plate, which, copied from the best reconstruction I could 

 formerly give of the species, gives an incorrect idea of all but the general proportions. 

 The fulcrum-points of the axis, &c., are also imperfect, so we had better erase the figure 

 entirely. It is not very pleasant to admit so many errors, but it is a shorter plan than 

 trying to defend or excuse them. The description in page 135 is more correct; but 

 the glabella is not so wide as the cheeks, nor the axis of the thorax as the pleurae ; and 

 these latter have the fulcrum placed at less than one half out instead of two-thii'ds. The 

 pleural- groove is nearly straight, only a little sigmoid ; and the tips are truncate, not 

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