“I had at first,” says Agassiz, “connected with pterichthys the only species known of that genus, by calling it _pterichthys hydrophilus_, but a more profound study and attentive comparison of that species with the genus coccosteus, have proved that it ought to form a distinct genus, intermediate betwixt pterichthys and coccosteus, which I have named _pamphractus_, in consequence of the divided form of the carapace. The pectoral fins of pamphractus resemble very much those of the pterichthys in their form, being slender, elongated, and crooked (courbée). But the plates of the carapace are all differently arranged. The central plate is very large (énorme); it covers two-thirds of the whole carapace, and unites the anterior articulation of the head with the carapace. The lateral plates, which acquire so great a development in the pterichthys, are here reduced to narrow stripes, stretching to the edge of the carapace; while, on the other hand; the posterior plates are of very great size, and form with a small intercalated plate the extremity of the carapace. The disposition of the plates of the head is likewise very different from that of the pterichthys, in which we discern no thoracic cincture as in that genus, but a transverse line, which separates in a striking manner the plates of the head from those of the carapace. _We see not any portion of the tail_; but I presume that it would bear a resemblance to the form of that of pterichthys.” Agassiz thus concludes his description of pamphractus, which we have partly abridged:—“The excessive development of the central plate of the carapace which reaches the articulation of the head—the absence of a thoracic cincture making the round of the body—and the distinct separation of the occipital articulation, will always distinguish this genus from that of pterichthys.”