14 BRITISH PERMIAN BRACHIOPODA. 



ribs are also at times of unequal width, even on the same example ; and the entire surface 

 of the shell is ornamented by close and regular scale-like, concentric, imbricated laminae. 



In the interior, the spiral cones fill the larger portion of the shell, as may be perceived 

 by a glance at the illustration (PI. I, fig. 27), drawn from a beautiful specimen in the 

 collection of Mr. Kirkby. The principal lamellae are here attached, as in all Spiriferas, to 

 prolongations departing from the base of the inner socket walls. 



The shell-structure has been stated by Professor King to be minutely punctuated, but 

 neither Professor M'Coy nor myself have been able to recognise any trace of those tubular 

 perforations ; x nor does the interior itself present those peculiarities which accompany the 

 perforated test of Spiriferina. The interior of the ventral valve does not show a trace of 

 that elevated mesial septum which is always present in Spiriferina cristata, Sp. octoplicata, 

 Sp. Milnsteri, rostrata, Tessoni, and other forms composing that sub-genus. The dental 

 or rostral plates in 8. alata are also much smaller, and I might almost say rudimentary ; 

 the muscular impressions are likewise exactly similar to those peculiar to the genus 

 Spirifera. In the ventral valve the adductor (a) forms a small, lengthened, oval impres- 

 sion, apparently divided by a minute mesial ridge or raised line, and on either side of the 

 adductor are seen the larger scars left by the cardinal muscle (r) : these are well displayed 

 on the numerous internal casts found at Humbleton Hill, and of which PI. II, figs. 6, 7, 

 are illustrations. The ovarian spaces (o) are likewise clearly defined on most specimens ; 

 and some of the vascular markings have been described by Professor King. 



In the dorsal valve, under the extremity of the umbone, there exists a small striated 

 cardinal process or boss, but no hinge-plate, and a little lower down is seen the quadruple 

 impression left by the adductor (PL I, figs. 31, 32, 33 a). 



Professor King seems to have misunderstood the impressions visible on the 

 internal casts of this valve, for he describes the smooth space above the central pair as 

 the " posterior division of the valvular muscle," and our central pair as the " anterior 

 division of the same muscle," 2 thus placing one pair above the other, while in reality both 

 are situated almost on a level (figs. 32 and 33). If the reader will kindly refer to the 

 casts of the Carboniferous Spirifera trigonalis (Part V, PI. V, figs. 26, 27) he will perceive 

 how strikingly they agree with those of the Permian shell. It is, therefore, evident that 

 the internal arrangements alone denote an imperforated species. Most authors are now of 

 opinion that Sp. undulata, Sowerby, is only one of the numerous variations in shape of 

 Schlotheim's Sp. alata, to which I must certainly add one or two of Professor King's 

 illustrations of his Sp. Permiana (pi. ix, figs. 18, 19, and 20). 



The study of a large number of specimens of Sp. alata, collected by Messrs. Howse 



1 Dr. Carpenter has examined the intimate shell-structure, and, having scaled off large flakes from a 

 •well-preserved specimen (a thing that could not be done to any perforated shell, as it does not split thus 

 into laminae), he did not find the least vestige of anything that could be called perforations, the shell- 

 structure being in all respects analogous to the Rhynchonella type. 



2 ' Monograph,' page facing pi. ix, fig. 6. 



