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Show 58 PROF. F. J. B E L L O N T H E [Feb. 19, These additions have, as may be supposed, led me to a careful study of the generic and specific characters of these forms ; a work in which, unfortunately, one has been able to gain but little assistance from preceding naturalists. The only writer who stands in the front rank of the students of Oreaster is'Dr. Liitken \ and of his work, unhappily, I have been unable to make as full a use as I should have done had he written in a language whose literature was rich enough to justify the time necessary for learning it, or in case I had understood a language which, when all is told, is not spoken by a population exceeding one half that of this metropolis. I have, however, this satisfactory reflection, that in all, or nearly all, the cases in which I have been able to understand him, there is complete agreement between us. In the course of the paper I make use of some technical terms, which are either new or have been but little used ; and in so doing I fear I shall bring on myself the wrath of Mr. Lyman for forcing the reader to undergo a certain amount of " sawdust swallowing" 2 ; but I shall, I believe, thereby adopt a method which is not only approved by the philosopher and logician 3, and adopted by experts in every branch of art and science, but one which will aid in the two objects that ought now to be very dear to all zoologists-(a) the condensation and assimilation of our technical descriptions, and (fi) the preparation for a systematic method of formulation, by means of which intellectual operations may be rendered more easy and more rapid *. It is convenient to have a single term for the line which divides the dorsal surface of the arm into two'halves ; where this line is most apparent it has the form of a ridge, and I propose therefore to speak of it as the lophial line, and of its spines as the lophial spines. The five, often prominent, spines which are found at the proximal end of the lophial lines may be called the apical spines, while the term apical region may be well applied to the area contained by the lines whicb join them to one another. I have seen no reason for departing from the use of the definite terms superomarginal and inferomarginal for the upper and lower series of marginal plates; nor can I propose any change in the terms for the adambulacral spinulation (monacanthid, diplacanthid, and triplacanthid) which I suggested in the first of these " Contributions5." Before commencing a systematic study of the species of this genus it is necessary to make oneself acquainted with the character of the modifications which the species undergo during growth. Not only is it necessary to do this for the purpose of correctly discriminating specific forms, but it would appear to be the mode 1 Videnskabelige Meddelelser (Copenhagen), 1859, 1864, 1871. 2 See his Introduction to his Eeport cn the Ophiurids of the ' Challenger.' 3 See Mill, Logic, 4th ed. ii. pp. 245-6. 4 Cf. Owen, Phil. Trans. 185U, pp. 496-497; and Allinan, Rep. Brit. Assoc. 1863, p. 352. 6 P. Z. S. 1881, p. 499. |