I have examined a great number of specimens from various localities, taken at different times of the year,--some dozen specimens from Cornwall,[53] and several from unknown localities in various collections; some from Ireland, from the Shetland Islands, from Norway, and from near Naples. Every one of these specimens, with the exception of some of the Neapolitan ones, had parasitic males attached to them: I must also except very young specimens, on which they never occur. On a Cornish specimen, with a capitulum a little more than one fifth of an inch in length, it may be mentioned as unusual that there were three males. In young specimens there is generally one male on each scutum, but sometimes there are two, and sometimes none on one side. In large old Cornish specimens I have counted on the two sides together, six, seven, and eight males, and in one Irish specimen no less than ten, seven all close together on one valve and three on the other, but I do not suppose that all these were alive at the same time. In the Neapolitan specimens, however, which are the largest that I have seen, there was in no case more than two; and out of seven or eight specimens, four had not any male; so that it would appear there is something in this locality hostile to the development of the parasitic males. I have noticed only one instance (that given in fig. 9) in which the males were imbedded a little way apart; generally they touch each other, and are cemented together: where there are several males, they occur at different levels, as measured from the under or upper surface of the chitine border: in one instance of four males adhering to one valve, I distinctly perceived that the lowest one was white, pulpy, and recently attached; the two above, which were placed close together and between the same laminæ of chitine, were mature; and the third still higher up, was dead, empty, transparent, and half decayed: in some other instances, I have found the uppermost parasites dead, and, together with the surrounding chitine, partially worn away. [53] I am greatly indebted to Mr. Peach for his unwearied kindness in procuring me fresh specimens. Mr. W. Thompson allowed me to dissect one, possessing particular interest, out of his three Irish specimens. Professor Forbes procured me a specimen from the Shetland Islands, and Professor Steenstrup was so kind to take pains to send me some Scandinavian specimens.