TRINUCLEUS ? MACCONOCHIEI. 11 



well as of the cheeks in the adult is smooth, as Barrande states. From interna] 

 casts of adults there is also no evidence that the inner surface of the shell was 

 always reticulate. The outer surface of the smaller and presumably immature 

 specimens is also smooth, but the inner surface in some of these young individuals 

 is minutely pitted or reticulate, and it is probable that the ornamentation like the 

 " ocular " tubercle disappears with age. Barrande notices a reticulation in some 

 specimens, but it is not taken by him as characteristic of the species. 



The variations in the development of the fringe which are due to age are 

 correctly noticed by Nicholson and Etheridge, but it may be added that the older 

 individuals have the outermost row of pits larger and more elongated than the 

 others, and in some cases these contain not only two but even three pores in a 

 line. With regard to the pygidium, the first six transverse furrows across the 

 axis have a deep pit on each side in the axial furrows, as partly indicated in one 

 figure (M., pi. xiii, f. 13) but not mentioned in the text. 



The identity of the Girvan form with the Bohemian T. bucldandi seen is to be 

 beyond doubt, as a comparison with some of Barrande's specimens shows ; but 

 with respect to T. bucldandi being a variety of T. seticorms, His., I am not at all 

 satisfied with the evidence or arguments of Nicholson and Etheridge. Nor do I 

 consider it sufficiently demonstrated that the adult form of T. seticomis is 

 equivalent to the young or middle-age stages of the Bohemian T. bucldandi. It 

 appears to me better for the present to keep the Grirvan form apart from that 

 known as T. seticomis, especially as there still exists some confusion in the 

 interpretation of the latter species in the British Isles. 



The Girvan examples of T. bucldandi reach an unusually large size for in- 

 dividuals of Trinucleus, some of the head-shields measuring nearly 20 mm. in 

 length without reckoning the genal prolongations of the fringe. 



Collections.— Mrs. Gray (f. M.) ; Edinburgh Museum; Museum of Practical 

 Geology, Jerniyn Street; British Museum; Woodwardian Museum; Hunterian 

 Museum, Glasgow. 



Horizons and Localities. — Druniniuck Group (U. Bala) : Drummuck and Thraive 

 Glen ; Starfish Bed, Lady Burn. 



2. Trinucleus ?macconochiei, Etheridge and Nicholson, 1879. 



1>s7'.i. Ampyx ! macconochiei, Etheridge and Nicholson, Mon. Su. Foss. Grirvan, fasc. ii. p. L83, pi. \i\. 



fig. 1. 

 1880. Trinucleus macconochiei, Etheridge and Nicholson, Mon. Sil. Foss. Girvan. fasc. iii, p. 288, 



pi. xix. fig. 9. 

 1899. Trinucleus macconochiei, Mem. Gfeol. Surv., Silur. Rocks Brit., vol. i. Scotland, pp. 509, 674, 689 



Specific Characters. —General form broadly oval. 



