TEREBRATULA. 215 



could produce between T. hastata and T. sacculus. Look, for example, at the deeply 

 biplicated example (fig. 9) and to that without any Implication at all (fig. 11) of the plate 

 above quoted ; still both have been recognised by Palaeontologists as belonging to a single 

 species, and to be intimately connected by every degree of modification. I may also, 

 while upon this subject, again remind the reader that out of many thousand specimens of 

 T. biplicata, collected near Cambridge, but one (fig. 6) showing remains of colour has been 

 hitherto procured, and whose markings very closely resembled those of our carboniferous 

 T. hastata. 



T. Gillingensis, in its extreme form (PI. XLIX, figs. 19, 20), appears different enough 

 from the usual shapes of T. hastata, but we must not consider extremes alone, but rather 

 the character presented by the larger number of individuals, and then we will soon find 

 every intermediate shape by which these extremes may be connected with Sowerby's species. 



T. vesicularis also, with its deep triundate front, is certainly very peculiar, but this is 

 not the common condition of the generality of specimens, which indubitably by gradation 

 assume the characteristic shapes of T. sacculus and T. hastata. It is quite evident that in 

 both of the last-named forms there exists at times a tendency to the production of a small 

 central undulation or rib near the front of the dorsal valve, but the frontal margin of the 

 shell may be, and indeed very often is, triundate, without necessitating the production of 

 a median rib. The intimate connexion between T. hastata with its straight frontal margin, 

 and the T. vesicularis shape with deep triundate or triplicate dorsal valve, or frontal margin, 

 has been furnished by a small limestone quarry at Bowertrapping, near Dairy, in Ayrshire, 

 and of which variety a series of specimens have been carefully represented in PI. XLIX, 

 figs. 21 to 26. In this locality the T. vesicularis shape has attained very large proportions, 

 while in Yorkshire an exactly similar series has been found, but with much smaller propor- 

 tions ; still the Yorkshire T. vesicularis is a miniature fac-simile of the large Bowertrapping 

 variety, and in both these cases these extremes merge into the common shape of T. 

 hastata or of T. sacculus. — As to the other synonyms, I am still of opinion that T. feus, 

 M'Coy (p. 13), should be considered a very convex specimen of T. hastata, in which the 

 frontal margin is slightly triundate; and in PI. I will be found many examples of Sowerby's 

 species with or without a mesial depression in either valve ; and this leads me to observe 

 that the Permian T. elongata is in all probability, and T. sufflata certainly, a recurrent 

 form of T. hastata and T. succulus, and in proof of which I would beg the reader to cast 

 his eye at PI. LIV, figs. 1 and 2, 3 and 4, of this Monograph, and he will surely be 

 struck by the close resemblance of the figures of T. hastata and T. elongata represented 

 therein. The interior details, loops, &c, are exactly similar in all the forms of Terebratula 

 here described, and their animal was no doubt so likewise. 

 One mistaken synonym must, however, be corrected. 



At p. 1 Atrgpa virgoides, M/Coy, was supposed to be a form of T. hastata, and to 

 this species is certainly referable the Seminula virgoides represented at PI. 3 D ' fig. 23, of 

 M'Coy 's ' British Palaeozoic Fossils,' but the true Atrgpa virgoides, described and figured in 



