TEREBRATULA. 11 



It is not very difficult to find a number of examples presenting all these differences ; 

 but again it would be as easy to procure others which, from their intermediate character, 

 leave one in the greatest doubt as to which of the two they should be referred ; thus a 

 vast number of sufflata present not a trace of sinus or sulcus in the ventral valve, both 

 being regularly and equally inflated. Some also vary considerably in their depth, and 

 with smaller proportions, resemble the two large adult examples of T. elongata, illus- 

 trated in our plate (PI. I, figs. 5 and 18) ; and I can compare them to nothing better than 

 to the differences we would perceive between a tall, thin, and a short, thick, stumpy man, 

 the first representing T. elongata, the second T. sufflata. 



Professor King is of opinion that T. sufflata closely resembles the Carboniferous T. 

 sacculus of Martin ; and, having kindly forwarded for my examination a specimen of both, 

 they appeared to me undistinguishable ; but having compared a numerous series of the 

 Carboniferous and Permian varieties of T. elongata, sufflata, and sacculus, I could perceive 

 in none of the Permian specimens the depression which commonly exists near the front of 

 the dorsal valve of most individuals of the Carboniferous species ; there remains but 

 little doubt as to the intimate resemblance existing between certain examples of Martin's 

 and Schlotheim's shell. T. elongata is certainly specifically distinct both from T. hastata 

 and sacculus ; and if we are to consider T. sufflata as a var. of elongata, then the individual 

 similarity presented between some young examples of sacculus and sufflata cannot be con- 

 sidered of paramount importance, as the general facies of the species would be very 

 different ; but if, on the contrary, T. sufflata is to be considered as specifically different 

 from T. elongata, then it would become a delicate question to determine whether sufflata 

 is in reality more than a variety or race of Martin's T. sacculus} 



Loc, 8fc. Both T. elongata and its var. sufflata are common to the same beds and 

 localities. It is also one of our commonest English Permian species in the shell limestone 

 of Tunstall-hill, Humbleton, Ryhope-Fieldhouse farm, Hilton Castle, Clack's Heugh, 

 Dalton-le-dale, &c. It has also been found in the magnesian conglomerate of Tynemouth. 

 On the Continent it is common to several localities — Corbusen, Possneck, &c, in Germany ; 

 at Nikefur, Orenbourg, Ilschalki, &c, in Russia. 



1 Professor King observes, while describing Ter. sufflata, that he has elsewhere stated that " this species 

 appears to be identical with a shell found in the mountain limestone of Bolland, probably hitherto considered 

 a var. of T. sacculus, a distinct, although closely allied species (' Monograph,' p. 150). M'Coy supposes 

 that the shell here referred to is identical with T. virgoides, but this is not the case. The Bolland specimen, 

 noticed under the last head as resembling T. elongata, has more affinity to M'Coy's species. I have been 

 led to re-examine the shell found in the neighbourhood of Bolland, and I cannot but say that it agrees most 

 remarkably with some specimens of the Permian species, particularly the testiferous one represented under 

 fig. 7, pi. vii, of my ' Monograph.' On the other hand, there are specimens figured on the same plate 

 closely approximating to true forms of T. sacculus in its mesial depression and emarginate front. The only 

 difference I perceive between the Bolland shell alluded to and the Permian fossil quoted is, that on the 

 former there are faint traces of longitudinal lines on the anterior half of the valves. I perceive nothing of 

 the kind on any of the Permian forms, nor do I recognise any on normal specimens of T. sacculus : 



