Ctenobranchiata (PECTINOBRANCHIATA, AN I SO BRANCH I AT A)

Sub-order of Gastropod a, having a large pectinate gill on the left side, and a rudimentary gill or olfactory organ. A spiral shell is usually present; most are carnivorous and po e a proboscis. A male intromittent organ is present. The has these divisions: Rhipidoglo a, Ptenoglo a, Rha nal strain. When such a bar (which originally showed the fibrous appearance at the fracture which accompanies tough iron) is suddenly broken in service, it is apt to exhibit a crystalline appearance at the break. The adherents of the first theory would thereupon conclude that it had broken because it had changed from fibrous to crystalline. The difficulties of this theory are, in brief, (1) there is no such thing as a fibrous structure in iron; (2) the change from one structure to another cannot occur in the cold solid; (3) the same bar may be made to show both types of fracture by varying the method of the break. A better theory explains these phenomena as the effect of combination with the metal of the uncombined carbon present. This will occur under jerk, jar, or shock, and, hardening the metal, renders it le able to stand sudden loads, and opens its grain, or makes it more coarsely crystalline.