456 CHARACTERS OF PALEOZOIC FISHES COPE. 



(.'iKiinlH'r liave a j^reuter deptli in proiJOition to the width and length of 

 the sknll than in the former. They may be characterized as follows: 



Posterior nnchal depth ^th widtli and yth lengtli of skull above; 

 M. rapkeidolahis ; fig. 4. 



Posterior nuchal depth entering width behind 2h times and length 

 4f times; M. mtllit'a)i,tii ; fig. 5. 



The skull of the M. sulUvantii is rather narrower than that of the 

 M. rapheldolahis. 



The half width at the foromam magnum enters the length to the 

 anterior border of the lateral marginal fossa 3.^ times, while it enters but 

 3 times in the M. rapheidolabis. 



IV — On the PECTORAL LIMB OF THE GENUS HOLONEMA NEWBERRY. 



Described from fragmentary or single plates by Claypole and New- 

 berry, the llolonema rugosa Claypole remained a vertebrate of uncertain 

 aftinities. At the meeting of the American Association for the Advance- 

 ment of Science held at Indianapolis, August, 1890, Prof. H. S. Williams 

 exhibited photographs of the posterior part of the carapace of a newly 

 discovered specimen, which includes the greater i)art of the two median 

 dorsal plates and the posterior laterals. The rounded i)osterior out- 

 line of the carapace is similar to that seen in Bothriolepis, and neither 

 this nor any of the specimens described up to that time demonstrate 

 the distinctness of this form from that genus. 



In the collection of Mr. R. D. Lacoe, of Pittston, Pennsylvania, 

 which that gentleman kindly jdaced at my disposal, there are speci 

 mens of this genus from INIansfield, Tioga County, Pennsylvania. Tlie 

 hirgest of these is a lateral plate of the plastron, partly represented by 

 a very distinct mold of the matrix. It measures 190 millimetres in 

 length and 105 millimetres in width. Besides this, there is a nearly 

 C()nn)lete pectoral spine, whi(;h is of much interest, as this part of the 

 skeleton has not been previously known. (Fig. 7.) 



This spine belongs to a smaller individual than any of those of the 

 llolonema rugosa yet described, but until the range of dimensions of 

 that species is known it will not be safe to regard it as representing 

 another species. The range of si/e of the Botkriolcpis canadensis is very 

 considerable. The spiiu' differs from that of both Bothriolepis and 

 Pterichthys in being without complete segmentation. It is continuous 

 throughout to the apex. This, then, will constitute the generic distinc- 

 tion so far known between Holonema and Bothoiolepis. The tissue of 

 the spine is disposed in tessera), as in the other genera allied. A single 

 series of three elongate narrow hexagons extends down the center of 

 the external face, and the lower space is divided by sutures, wliich 

 extend from the lateral angles of the hexagons to the border of tiie spine. 

 The apex of the si)ine from the last hexagon, and lor a length nearly 

 equal to it, is not tessellated. 



