BRITISH DEVONIAN BRACHIOPODA. 15 



extremities facing each other. The branches of the loop diverge to about half their 

 length when they rapidly increase in width and converge until they join, forming thus in 

 the lower half of the loop a broad, inclined, transverse band with a pointed extremity in 

 front. There is a slight longitudinal depression on the dorsal or convex side of this 

 broad band where the two lamellae join, and corresponding with this depression there is, 

 on the other side of the band, a thin projecting ridge or plate, which sometimes extends 

 backwards for some distance towards the ventral valve (but having no connection with 

 it) and upwards between the two branches of the loop as they diverge from the hinge- 

 plate. 



Obs. — In 1841 Phillips briefly described the exterior characters of this species, and 

 gave it the name Terehratula virgo. Knowing nothing of its interior characters, and 

 never having seen a specimen of the shell, at p. 6 of my ' Devonian Monograph ' I 

 erroneously supposed it might be a synonym of T. sacculus, from which it is, however, 

 generically and specifically distinct. 



Some time in 1880 Mr. Whidborne drew my attention to this species, sending me 

 several specimens, and intimating that he believed it to be specifically distinct from 

 T. sacculus. He also forwarded to Mr. Glass a number of specimens, which Mr. Glass 

 lost no time in operating upon. Many, indeed, have been his endeavours, conducted 

 with great skill and patience, to work out its internal characters. The matrix filling the 

 shell being a seraiopaque sparry limestone, it was exceedingly difficult to work the 

 specimens so as to clearly expose the loop, especially by means of transparency ; never- 

 theless, after sacrificing dozens of specimens, he succeeded in exposing the loop in several 

 examples as I have described and figured it. 



Mr. Glass says, that, whilst he has only sent me a few preparations showing the loop 

 as I have figured it, he has found exactly the same shape of loop in all those specimens 

 he has operated on, which were in a condition to show the interior, and that such 

 specimens have been very many. The majority of specimens used up, he says, were 

 destroyed by his continued attempts to show the exact extent and shape of the 

 projecting plate. He thinks that in many of the specimens the plate referred to 

 has, as I have figured it, only a slight projection into the ventral valve, but that 

 in some cases it evidently extends for some distance in this direction, as well as 

 upwards between the two lamellae composing the loop. Though Mr. Glass has not been 

 able, from the Lumraaton specimens, to determine the exact shape of this plate, it has 

 been described, as we shall see further on, by Prof. Winchell. 



Mr. Glass thinks that it is perfectly certain, from the many specimens upon which he 

 has operated, that there is no reflected ribbon-band in Centronella similar to that which 

 exists in Waldheimia and other loop-bearing species of Terebratulidae. Professor 

 Priele, Mr. C. Moore, and myself have found that in some loop-bearing Brachiopoda, 

 such as Waldheimia cranium, the young specimens have the primary branches of the loop 

 united in the middle to a narrow ridge or plate, but in these cases the reflected portion 



