8 



BEITISH FOSSILS. 



are in 6 rows (5 in younger specimens), of which the outer two are placed close 

 together in the deep furrow immediately before the thickened striate margin. The 

 concentric rows are more distinct than the radiating ones in Bala specimens, — in 

 those from Haverfordwest and Ireland the radiation is more manifest. The 

 specimens from the latter locality show the same reticulate character of surface of 

 the head which is seen in our next species. This structure is but rarely to be seen 

 in our other specimens, — nor can we find it at all in two from Sweden in the collec- 

 tion of the Geological Society. Perhaps it is easily abraded ; the specimens agree 

 in all other respects. 



Localities. — Lower SiLimiAisr. In Ireland .; Desertcreat, Tyrone ; Chair of Kildare ; 

 Newtown, Wexford. In Wales ; Bala ; Llanfyllin ; Haverfordwest, &c. ; chiefly 

 in limestone strata. 



Foreign Localities. — Lower Silurian. Dalecarlia. Koenigshof, Bohemia (Barrande.) 



5. T. jimhriatus, Murchison, Sil. Syst., t. 23. fig. 2 (head only.) Ampyx (^Cryptolithus) 

 fimbriat,^MMR. (1839), 52. (not of Portl.) Tretaspis, M'Coy, Pal. Poss. 146. pi. 1 E. f. 16. 



T. late ovatus depressus, capite truncato, undique reticulato-punctato ; glabella con- 

 vexiusculd, genas longitudine cequante sed angustiore, utrinque sulcis tribus brevibus ; fimbria 

 subtus concava ; insuper primum plana radiatim sulcata, deinde angulatim deflexa ; parte 

 plana radiatim sulcata, poris in utroque sulco 4 ; parte externa ad marginem singula pororum 

 serie ornata ; angulis capitis haud expansis, spinis brevibus tetragonis divergentibus ; thorace 

 abbreviato ; cauda thorace breviore, subtriangulatd, lateribus loeviter 5-costatis, marglni declivi. 

 A specimen of this species in the young state, 2 lines long, has been found with only 

 5 thoracic segments ; it however soon attains the full number. The head is very 

 wide : the fringe is very regular in width round the head, and not invaded at all 

 in front by the glabella as in the last species. It is flat and deeply marked for 

 the first half with sunk radii, fall of close-set pores, then rather abruptly deflected 

 and furnished with but a single row on the outer portion. 

 The tail figured on the same slab with the head of this species in the Sil. Syst. belongs 

 to Ampyx nudus ; and Burmeister has described it as belonging to the present 

 species ; the true tail is short and few-ribbed, as in all the other Trinuclei, 

 Localities. — Only yet found at Builth in Radnorshire ; it is exceedingly abundant in 

 the lane leading to the farmhouse called Pen-Cerrig, on the west side of the hiU, 

 where it occurs with Ampyx nudus and Agnostus M^Coyii, {A. pisiformis, Murch.) 



6. T. radiatus, Murchison, Sil. Syst., t. 24. fig. 3. Ampyx, Emmr. 1. c. 52. (not of Port- 

 lock, Geol. Rep., nor of M'Coy, Pal. Poss. 146). 



T.paullo adhuc cognotus; prcecedenti simillimus, nisi angulis superioribus capitis expansis 

 multipunctatis, glabella longiori. 



Except in the expanded upper angles of the fringe, which consequently contain at 

 this part many more pores in a row, this does not appear to differ from the last 

 species. The style of the fringe is exactly similar, and the pores placed in furrows 

 in the same way. 



The enlarged angles are the chief character, but in some specimens of T.fimbriatus 

 there are slight indications of this. As T. concentricus varies in this respect it is 

 not too much to suppose T. radiatus to be a variety in the same way. The spines, 

 however, are less divergent, and the fringe is invaded in front by the glabella, which 

 too is longer in proportion. In this species not all the pores appear to penetrate 

 the fringe ; the outermost and innermost certainly do ; the intermediate ones, if 

 they do pierce through, are smaller. 



Locality. — Trilobite Dingle, Welshpool [Sir R. I. Murchison.] Coll. Geol. Society^ 



J. W. Saltee. 



August, 1853. 



