Belt — On the Fauna of the *^Lingula Flags'' 11 



very sparingly, along with A. trisectus, A. princeps, and the other fossils of the black 

 shales. 



Agnostus trisectus, Salter. 



This species, described from, imperfect specimens of the pygidiura, occurs in 

 great abundance in the black shales at Rhiw-felyn, where I have obtained numerous 

 perfect specimens, a complete series of which is now deposited in the British 

 Museum. These show that, like A. princeps, it was furnished with marginal spines 

 Lo the pygidium ; and other close resemblances make it most difficult to dis- 

 tinguish some of the specimens from that species, with which, however, I hesitate 

 at present to join it, especially as the able author of the Monograph on the Trilo- 

 bita has announced his intention of dealing with the AgnostidcB, in the next part of 

 that valuable work, 



Agnostus Barlowii, spec. nov. (PL 11. Figs. 17, 18). — Length Jin., 

 breadth ^in. Oblong, ovate. 



Head rounded, ovate, plain, rising from all sides to a point near the base, Margin 

 very narrow. 



Thorax of two rings. Axis trilobate. 



Pygidium, shaped like head, rising to a central point near the base, with two slight 

 indentations, marking the commencement of an obsolete axis. 



This species resembles Angelin's figures of his A. glandiformis and A. hituhercu- 

 latus, but differs in the absence of tubercules, and in its trilobate thoracic axis. To A. 

 nudus, Bar., it comes still nearer, but that species has neither the axial furrows of 

 the pygidium, nor the trilobate thoracic axis of A. Barlowii. 



It is a striking example of the persistence of type amongst the Agnostidce, that 

 the nearest known ally of A. Barlowii, which is a Tremadoc form, should be a 

 species from the Lower Cambrian rocks of Bohemia. 



It occurs in the Lower Tremadoc beds near Rhiw-felyn, along with Asaphus inno- 

 tatus, Niobe Hovifrayi, Conocoryphe? depressa, etc., where it was first found by Mr. J. C. 

 Barlow, of Birmingham. This species comes from rocks a little beyond the limits of 

 this paper, but I include it, as it is the first example of Agnostus from British Tremadoc 

 strata, and for the purpose of commemmorating the services of Mr. J. C. Barlow, in 

 elucidating the geology of the Dolgelly district. 



BelleropJion Cambriensis, spec. nov. (PL II. Figs. 19, 20.) 

 Broadly involute with three or four distant, coarse ridges of growth, crossed by 

 faint longitudinal striae ; keel narrow. 



The discovery of this species carries the range of the Heteropodous Mollusca much 

 lower down in the Cambrian rocks than was before known. I first found it near 

 Craig-y-dinas, but have since discovered that it is not uncommon along with Cono- 

 coryphe? bucephala and Hymenocaris vermicauda, wherever the Upper Festiniog rocks 

 are exposed as on Mynydd-gader, and at Gwern-y-barcud, near Penmaen-pool. 



EXPLA'NATION OF PLATE II. 



Figs. 1-6. Conocoryphe? bucephala, spec, nov., from specimens in British 



Museum and collection of Thos. Belt. 

 „ 7-11. Conocoryphe? Williamsonii, spec, nov., from specimens in British 



Museum and collection of Thos. Belt. 

 „ 12-14. Conocoryphe? longispina, spec, nov., from specimens in British 



Museum and Museum Practical Geology. 

 „ 15, 16. Agnostus obtusus, spec, nov., fiom specimens in British Museum. 

 „ 17, 18. Agnostus Barlowii, spec, nov., from specimens in British Museum 



and collection of Mr. J. C. Barlow, of Birmingham. 

 „ 19, 20. Bellerophon Cambriensis, spec. nov. Both specimens figured are on 



one slab in British Museum. 



ERRATA. 



In Part I., page 495. Table of the Cambrian rocks. Obolella should have been 

 marked present in the upper part of the Dolgelly group and lower part of the 

 Tremadoc group, and Discina in the lower part of the Tremadoc group. 



In Part II., page 540, line 18 from the bottom, for Conocoryphe micrura, Sal., read 

 Conocoryphe? bucephala, spec. nov. 



