Bracutopopa. | LOWER PALZZOZOIC MOLLUSGCA. 191 
DiscinaA? sTRIATA (Sow.) 
Ref. and Syn.= Orbicula id. Sow. Sil. Syst. t. 5. f. 12. 
Sp. Ch.—Rotundato-subtrigonal, tumid; beak obtuse, marginal; surface slightly glossy, corneous, 
radiated with minute, close, subequal, prominent, rugged strize, about fifteen in one line at the margin. 
Width six lines, proportional length =, depth =. ; 
The genus of this fossil seems very doubtful; the two specimens I have examined (if Discine) had 
undergone an oblique distortion, and from having the beaks nearly in contact resembled the two valves of 
a lamellibranch. There are a few irregular concentric wrinkles. 
Position and Locality.—Upper Ludlow rock of Benson Knot, Kendal, Westmoreland. 
dth Family. SPIRIFERID/. 
Arms probably with long fimbriz, incapable of extension, and fixed to internal testaceous spirally-rolled 
apophyses ; shell calcareous, fibrous, or punctured. 
The family contains the following genera:—1, Spirifera; 2, Spiriferina; 3, Athyris; 4, Spirigerina. 
Genus. SPIRIFERA (Sow.) 
= Delthyris (Dal.) = Choristites (Fisch). 
Gen. Char.—Transversely oval, gibbous, radiatingly-ridged; hinge-line as long as the shell is wide; 
area nearly parallel-sided, of moderate width in the receiving* valve, very narrow in the opposite one; shell 
fibrous, foramen notching the area of both valves, that of the entering valve open, that of the receiving 
valve with an internal pseudo-deltidium bordered by two strong diverging, dental lamellz in the receiving 
valve, and by the flattened bases of the spiral apophyses in the other, which also usually shews a small 
mesial septum: casts of receiving valve are trilobed towards the beak, the small middle lobe being defined 
by the ends of the diverging dental lamellz on each side, its rounded end (analogous to a pseudo-deltidium) 
as well as those of the lateral lobes being formed by an inner layer of shell, between which and the external 
one is a wide hollow space. The muscular impressions of the great valve are shallow, radiated just within 
the ends of the dental lamellz: those of the entering valve (in the Permian S. adatus, and the Silurian 
S. Lynx) resemble those of Orthis, the four impressions being rounded and grouped together on the rostra] 
half of the middle, their boundaries forming a more or less distinct crucial mark, depressed in casts. 
There are three sub-genera besides Spirifera proper. 
1. Sub-genus Cyrrra (Dal.)—General characters of Spirifera, but the cardinal area very wide, trian- 
gular, and confined to the receiving valve, nearly closed by an external pseudo-deltidium. 
* The shells of the Brachiopoda, not only differ from those of the Lamellibranchiata in haying one applied to the 
dorsal aspect and the other to the ventral aspect of the animal, but all are destitute of the ‘ligament? which connects the 
valves of Lamellibranchs to each other, and of the ‘cartilage’ which forces them open. ‘The valves of the Brachiopoda 
are either entirely unconnected, or adhere by the interlocking of the hinge teeth, and in the latter case we have the curious 
peculiarity of the beak of that valve called ‘dorsal’ by anatomists, and ‘ ventral’ by nearly all describers of shells, entering 
within the cavity of the large or perforated valve. This obvious peculiarity furnishes me with the terms ‘entering and 
receiving valves, which I hope may be generally adopted in future, instead of the terms ‘dorsal and ventral yalves,’ which 
have been so invariably used in the wrong sense by conchologists, that reversing them in accordance with anatomy would 
be productive of constant confusion, It has been suggested that the use of the internal loops and other apophyses of the 
Brachiopoda was by their elasticity to force open the valves, in the absence of cartilage; but it will be found that they 
do not even touch the valves when closed, and I found about three years ago on examining some uncleaned Terebratule, 
sent by Mr Jukes to the Woodwardian Museum, that this was really effected in a way unexampled in Lamellibranch bivalves, 
namely by the action of a pair of muscles, which arise from the middle of the perforated or receiving valve, and the tendons 
of which are inserted into the internally prolonged entering beak of the entering valve, which thus forms a leyer moving 
on the hinge teeth as a fulerum. 
