484 



SCIENCE, 



[Vol. IY., No. 95. 



soldiers and statesmen for many decades, the 

 Americans now seem ready to commemorate 

 their literary and scientific heroes. John Har- 

 vard and Abraham Pierson, whose real like- 

 nesses perished long ago, have risen in bronze 

 upon the greens at Cambridge and New Haven. 

 The statues of Joseph Henry and Benjamin 

 Silliman stand near the scenes of their activi- 

 ty. Examples like these should be imitated 

 throughout the land. Those who have rendered 

 great services to science and education should 

 receive due recognition from those who have 

 profited by their labors. Only let us pray to 

 be spared such commonplace monuments as 

 are to be seen in abundance in London. Let 

 us rather study the memorial statues which 

 have of late years been placed in the cities of 

 Germany, Holland, France, and other conti- 

 nental countries. Better no monuments than 

 those which give positive pain to the beholders, 

 and which will some day be lowered, like the 

 Iron Duke from his lofty arch, when taste and 

 skill are more highly developed. 



LETTERS TO THE EDITOR. 

 The oldest living type of vertebrates. 



It is necessary to add a little to the discussion of 

 Chlamydoselachus in order to give readers of Science 

 a just idea of the case as it now stands. On hearing 

 the evidence presented in my paper at the Philadel- 

 phia meeting of the American association, Profes- 

 sor Cope gracefully conceded that he had mistaken 

 the affinities of Didymodus, and agreed with me 

 in the conclusions that the two genera belonged to 

 different orders, and that, judging from the teeth 

 alone, the nearest known allies of Chlamydoselachus 

 were Cladodonts of the subearboniferous and middle 

 Devonian. The shapes of the bodies of the extinct 

 Cladodonts are yet unknown. What has been con- 

 sidered the closest approach to a determination of 

 their skeletal structure is that of Dr. Traquair, based 

 on the resemblance of a single, partly visible, and im- 

 perfect tooth of Ctenacantlius co>tellatus. Professor 

 Gill has accepted the doctor's idea, and classified the 

 sharks, fossil and recent, in accordance (Science, iii. 

 346). The lateral curvature near the apex of the 

 tooth is rather against the determination, and the 

 character of the base is not known. The weight of 

 the evidence does not seem to favor the conclusion 

 that Ctenacantlius is a Cladodont. The tooth re- 

 sembles that of Rhina as much. Until we are toler- 

 ably certain in regard to the extinct (the unknown), 

 it is about as well to assume that it in some degree 

 resembled the recent (the known). In a revision of 

 the arrangement of Gill, the Xenacanthini should 

 be taken from his Lipospondyli to form a new order, 

 the Cladodonts removed and placed with the Selach- 

 ophichthyoidi, and the definitions revised in several 



cases to accord with structure. The result would 

 appear thus : — 



Xenacanthini, Pleuracanthus, Didymodus, and allies, 

 prototypes of bony fishes. 



Selachia. Gakei. 



1. Lipospondyli, including the true Hybodonts, but 

 excluding the Cladodonts. 



2. Selachophichthyoidi, including Chlamydoselachus 

 and the Cladodonts, but excluding Didymodus; 

 changing the definition from " vertebral condition 

 unknown, and with teeth having fixed bases," to 

 " vertebrae partially or imperfectly developed, noto- 

 chord persistent, and teeth with broad backward 

 expanded bases." 



3. Opistharthri, the Notidanidae; changing the ex- 

 pression, " which alone exhibit these peculiarities 

 in the existing fauna," to read, " which share many 

 of their peculiarities with the preceding." 



4. Proarthri, Heterodontidae. 



5. Mesarthri (Anarthri Gill), most sharks; changing 

 the statement, " palato-quadrate apparatus not ar- 

 ticulated with the skull," to read, "pterygo-quadrate 

 articulated or connected with the skull in the orbit 

 by the trabecular elbow." The name 'Anarthri' 

 is manifestly inappropriate, since few of the gen- 

 era are without the articulation. 



6. Rhinae, Rhinidae; changing the definition so that 

 " with the palato-quadrate apparatus not articu- 

 lated with the skull " shall read, " with the pterygo- 

 quadrate articulated with the skull in the orbit by 

 the trabecular elbow." S. Gasman. 



Cambridge, Nov. 17. 



Water of crystallization. 



The first accompanying illustration (fig. 1) is taken 

 from a photograph of plumes produced by the crystal- 

 lization of water. In the appendix of Tyndall's work 

 on light will be found an illustration (fig. 2) of the 



Fig. 1. 



same phenomenon which is explained in the follow- 

 ing letter from the late Professor Joseph Henry to 

 Professor Tyndall. 



"Accompanying this, I send you a photograph at 

 the request of Prof. S. H. Lockett of the Louisiana 

 state university, of which the following is his ex- 

 planation: — 



" ' In my drawing-room I kept a wash-basin in which 

 to rinse out the color from my water-color brushes. 



