FROM THE OLD RED SANDSTONE OF SHETLAND. 327 



regards the first, there can be no doubt that his explanation of the facts known about 

 Holonema is by far the most probable one. 



Consequently we place Holonema in the order Arthrodira, though in what special 

 group or family it is still impossible to say. Whether Phyllolepis, the remains of 

 which likewise consist of thin plates with a rugose sculpture, also is referable to the 

 same order, remains for future discussion. 



Distribution. — Plates certainly referable to Holonema have hitherto been found in 

 the United States, and there only in strata of Upper Devonian age. The "Chemung" 

 rocks of the States of New York and Pennsylvania are cited as the source of these 

 specimens, for though Claypole first stated regarding Professor H. S. Williams's 

 specimen that it was from the " Catskill," he also said that " it is right to add that the 

 exact horizon of the fossils is a little uncertain. They came, however, from either the 

 highest beds of the Chemung or the lowest of the Catskill." 



Dr Smith Woodward, however, in his "Catalogue," part ii. p. 315, mentions that 

 "so far as can be determined from the description and imperfect figures, the dermal 

 plates from the Devonian of the Eifel named Coccosteus obtusus, Koenen, exhibit much 

 resemblance to those of Holonema." I have carefully read Professor von Koenen's 

 description # and examined his figures (the latter are certainly imperfect enough), but am 

 very doubtful as to the relationship to Holonema of the pieces depicted, especially as 

 their radiating striae are said to be " on the under side." The words are : " Diese Platten 

 zeigen einerseits eine unregelmassige feine Streifung parallel ihrem Aussenrande, und 

 andererseits auf der Unterseite eine feine von einem Puncte ausstrahlende Streifung, 

 welche indessen an je einer langen Seite sich steil gegen diese umbiegt." It would 

 be necessary to re-examine the originals to come to a definite conclusion on the 

 matter. 



Holonema ornatum, sp. nov., Traquair. PI. II. 



Specific Character. — The marginal radiating ridges are ornamented each with a row 

 of minute ganoid tubercles. 



Description. — Only two fragments have occurred. The first of these is represented 

 in PI. II. fig. 1, and is evidently a portion of what must have been originally a plate of 

 considerable dimensions. It shows the marginal band of ridges very well, but the 

 central part of the plate has come off with the counterpart. The band is about 

 1 inch in breadth, and consists of ridges which are mostly parallel with each other and 

 perpendicular to the free margin of the plate, except at one extremity (the upper in the 

 figure), where they are rather oblique. At the opposite extremity of the fragment a 

 small part of the central area is seen, and there the ridges become oblique and irregular. 

 Where they are regular, from nine to ten may be counted in the ^ inch transversely. 

 Each of these ridges is ornamented with one row of minute, rounded, brilliantly ganoid 

 tubercles. 



* Verh. naturh. Verein. preuss. Rheinl, vol. xliii. (1886), pp. 55-57, with two figures. 



