April 20, 1876] 



NATURE 



487 



that conditions favourable to observation in the northern 

 hemisphere occur. The "comet-seeker" properly so 

 called is an instrument much better known on the con- 

 tinent, and probably in America, than in this country. It 

 may be used for much other useful astronomical work, 

 and if the observer is content to be without equatorial 

 mounting, and rely upon star-maps for ascertaining ap- 

 proximate positions, a first-rate instrument of this class 

 need not involve great outlay. It is true, we believe, that 

 the fine comet-seekers of the kind produced by the con- 

 tinental opticians (those of Berlin and Vienna especially) 

 have, like most other things, increased in their cost during 

 the last twenty years or so, but less perfect instruments 

 would doubtless enable an amateur to do excellent work 

 in the above direction. 



TO FIND EASTER 



ANEW York correspondent sends us the following 

 rule, which he states to be devised by himself, to 

 find the date of Easter Sunday, perpetually : — 



To find Easter *^/or ever." 



Divide 



The year of our Lord 



>> >> 



b 



i + 8 



b-f+i 



19a + b - d -g + 15 



32 +2^ + 2 /-/^-^ 



o + llA+22/ 



h + /- 7/w -r 114 ... 



n is the number of the month of the year and o -f- i is 

 the number of the day of the month on which Easter 



falls, 



PROF. FLOWER'S HUNTER! AN LECTURES 

 ON THE RELATION OF EXTINCT TO EXISI- 

 ING MAMMALIA ^ 



VII. 



THE Carnivora, as existing at the present day, form a 

 natural group, though very sharply divided into two 

 distinct sections, the Pinniped or aquatic, and the Fissi- 

 ped or terrestrial forms. The former include the Seals, 

 Walrus, and Otaria or Sea-lions. They differ from the 

 terrestrial carnivora chiefly in moditications of their 

 limbs to suit a semi-aquatic life. In their dentition they 

 also present striking distinctions. Though they have the 

 small incisors, large, pointed, recurved canines, and more 

 or less trenchant molars characteristic of the order ; the 

 incisors depart from the typical number of three above 

 and three below on each side, so constant in the other 

 division, being always less numerous, and the molars 

 are simple and uniform in character, never having one 

 tooth differentiated as the sectorial, and others as tuber- 

 cular molars. The walrus offers a most remarkable 

 modification of dental organisation, which, being unac- 

 companied by any other deviation from the general struc- 

 ture of the group affords an important caution against 

 placing too great reliance in classification upon characters 

 derived from teeth alone. It must, however, be noted 

 that a knowledge of the complete dentition of this ani- 

 mal in its early stages shows a nearer conformation to 



I Abstract of a course of lectures delivered at the Royal College of Sur- 

 geons "On the Relation of Extinct to Existing Mammalia, with Special 

 Reference to the Derivative Hypothesis," in conclusion of the course of 1873. 

 (See Reports in Naturb for that year.) Continued firom p. 450, 



the general type than appears at first sight in an exami- 

 nation of the adult. The existing species of Pinnipedia 

 show some gradational forms between the most aquatic 

 species, and those (as the Otarice) which more nearly 

 resemble the terrestrial Carnivores, and upon the suppo- 

 sition that the former have been gradually differentiated 

 from the latter, it might be hoped that palaeontology 

 would have revealed some further stages in the series of 

 modifications. At present, however, this expectation has 

 been disappointed. In fact, the fossil remains of seals 

 and seal-like animals as yet known are not numerous 

 or of very great interest, although when those of the 

 Antwerp crags, where they occur more abundantly than 

 elsewhere, have been completely described (a work upon 

 which M. Van Beneden is at present engaged) we may 

 look for further information about them. At present 

 we know of fragments of skulls, jaws, and principally 

 isolated teeth assigned to Pinnipeds, from various Mio- 

 cene and Pliocene deposits in France, South Germany, 

 Italy, and Bessarabia. The genus Pristiphoca, was founded 

 by Gervais on a jaw found in the Pliocene marine sands 

 of Montpellier ; it belongs to a form apparently allied to 

 Stenorhynchus and Pelagius. The Miocene species from 

 Aquitaine, known only by isolated teeth, are referred by 

 Delfortrie to the genus Otaria. Tusks of animals of 

 great size, and apparently allied to the walrus, have been 

 found in the Antwerp and Suffolk crags, and received the 

 name of Trichechodoii, and a lower jaw of much interest, 

 as showing a transitional character between the walrus 

 and the more typical seals, also from Antwerp, has been 

 described under the name oi Alachtliertitin. 



The fissiped carnivora arc distinguished from the seals 

 by their limbs being adapted to terrestrial progression, 

 and by their dentition. The latter is best exemplified by 

 that of the dog, which is one. of the most average or 

 generalised forms of the order. Its dental formula is 



i £- c —p —m— = 42, thus only wanting the last upper 



3143 

 molar to complete the full typical mammalian dentition. 

 The premolar and molar series are much differentiated 

 from each other in characters, and one tooth above and 

 below is distinguished from all the others by its superior 

 size and special attributes, and hence called in descriptive 

 odontology the "sectorial" or "carnassial" tooth. Though 

 the upper and lower "sectorial" have some adaptive 

 similarity, and work against each other like the blades of 

 shears, they are not the homologous teeth, the upper one 

 being the fourth premolar and the lower one the first true 

 molar. The former consists essentially of a more or less 

 compressed blade, consisting of three cusps, and sup- 

 ported on two roots, and an inner lobe supported on a 

 distinct root. The anterior lobe of the blade is very 

 small, the middle one conical, high, and pointed, and the 

 posterior has a compressed, straight, knife-like edge. The 

 lower sectorial has two roots, supporting a crown, con- 

 sisting, when fully developed of a compressed bilobed 

 blade, a heel, and an inner tubercle. Great modifica- 

 tions in the characters of these teeth occur in the different 

 genera of the sub-order, recent and extinct, but their 

 essential similarity can be traced in all, though some- 

 times so disguised as to be recognised with difficulty. 

 The teeth in front of sectorials in both jaws are com- 

 pressed and pointed, those behind them broad and tuber- 

 culated. 



The existing genus Cam's, comprising the animals com- 

 monly known as dogs, wolves, jackals, and foxes, may be 

 considered as truly cosmopolitan, being distributed on the 

 American continent from Greenland to Patagonia, and 

 throughout the Old World, and even Australia has its 

 wild dog, though this may belong to a feral race, intro- 

 duced originally by man. True dogs have also been 

 found in a fossil state in Europe and North America, 

 throughout the Pleistocene, Pliocene, and even Miocene 

 periods. Many of these are only known by fragments and 



