PLACOGAMHDEI 127 



whole body. But generally, as in Pimeloclus, the hinder 

 muscular part of the trunk is undefended, as in Coccosteus. 

 The ganoid plates of the head and back shields are fretted 

 with rows or ridges of confluent tubercles, radiating from the 

 centre to the circumference of the plate, whilst the inner 

 surface is smooth, as in Coccosteus (fig. 46) ; and, moreover, 

 the dorsal plate in existing Siluroids sends down a median 

 ridge from its inner surface, like that from the " dorso-median " 

 plate in Coccosteus. The point of resemblance to be mainly 

 noticed, however, is the contrast furnished by the powerful 

 armature of the head and back with the unprotected naked- 

 ness of the posterior portions of the creature — a point specially 

 noticeable in Coccosteus, and apparent also, though in a lesser 

 degree, in some of the other genera of the old red, such as 

 the Pterichthycs and Asterol&pides. " From the snout of the 

 Coccosteus down to the posterior termination of the dorsal 

 plate the creature was cased in strong armour, the plates of 

 which remain as freshly preserved in the ancient rocks of the 

 country as those of the Pimelodi of the Ganges on the shelves 

 of the Elgin museum ; but from the pointed termination of 

 the plate immediately over the dorsal fin to the tail, com- 

 prising more than one-half the entire length of the animal, 

 all seems to have been exposed, without the protection of 

 even a scale ; and there survives in the better specimens 

 only the internal skeleton of the fish and the ray-bones of the 

 fins. It was armed, like a French dragoon, with a strong 

 helmet and a short cuirass ; and so we find its remains in the 

 state in which those of some of the soldiers of Napoleon's old 

 guard, that had been committed unstripped to the earth, may 

 be dug up in the future on the fatal field of Borodino, or along 

 the banks of the Dwina or the Wap. The cuirass lies still 

 attached to the helmet, but we only find the naked skeleton 

 attached to the cuirass. The Pterichthys to its strong helmet 

 and cuirass added a posterior armature of comparatively 



