50 



SCIENCE. 



IVol. IV., No. 76. 



number of species. The word ' yelk ' is spelled ac- 

 cording to the most approved usage throughout my 

 memoir, both Webster and Worcester agreeing in this ; 

 and I would commend to my critic's attention the re- 

 marks relating to this word to be found in the work 

 of the latter authority, where both Johnson and 

 Walker are also cited in favor of the same spelling. 



The expression of opinion by my critic as to the 

 relative value of previous literature is unfortunate. 

 Hoffmann's paper on the teleostean egg was cited for 

 the very good reason that it was undoubtedly the 

 most thorough and consecutive upon its special sub- 

 ject, which had appeared up to that time, or even to 

 the present. No American work can yet claim such 

 a distinction. 



The charge that I have ' padded ' my paper with 

 unnecessary quoted matter is unfair; for, out of one 

 hundred and eighteen pages of text, nine are taken up 

 with citations, — a proportion greatly exceeded in the 

 papers of many competent authorities. And I ask my 

 critic, in all fairness to me, if, by throwing out any 

 one of the quoted passages, the paper as a whole 

 would not lose in thoroughness and clearness of 

 statement; for the object of my paper was to give 

 a general statement of the facts relating to the 

 development of fishes, so that it might be safely re- 

 ferred to, especially as to the early stages. 



Whether my critic sees fit to accept my views upon 

 the layer which I have termed the ' yelk-hypoblast,' 

 is a matter of indifference to me. For his benefit, 

 I may cite the names of the following masters in 

 embryology, who agree with me more or less closely : 

 Vogt, Kupffer, Hoffmann, Rauber, Gensch, Ziegler, 

 and even, in one sense, His and Kolliker. 



John A. Rydeb. 



Smithsonian institution, Washington, D.C., 

 June 30. 



[Mr. Ryder will not find ' yelk ' used by the leading 

 embryologists, either in England or America; 'yolk' 

 being the form used by Huxley, Balfour, Allen Thomp- 

 son, Agassiz, etc. 'Embryology' is also similarly 

 employed, instead of ' embryography.' In our notice, 

 it was not said that either word was incorrect; but 

 we meant exactly what was printed, that they are a 

 'little eccentric' In regard to Hoffmann's paper, it 

 is by no means ' the most, thorough,' but contains 

 important errors. We fail to see how the value of 

 Hoffmann's paper is affected by American work 

 being considered less good. We regard Mr. Ryder's 

 own essay as much more valuable than Hoffmann's. 

 As to the padding, we think the charge fair that the 

 essay contains 'an unnecessary number of lengthy 

 extracts and abstracts : ' the latter Mr. Ryder ignores. 

 It is generally understood that very little editorial 

 supervision is exercised over most of our government 

 publications : hence they are often diffusely written, 

 and charged with much which might better be 

 omitted. We do not think that Mr. Ryder intention- 

 ally put in matter to fill out; but we do think he 

 failed to leave out much that he would have omitted 

 if his article had been for a carefully edited scientific 

 journal. As to the 'yelk-hypoblast,' the future will 

 decide between our opinions. 



Mr. Ryder is under a misapprehension, if he thinks 

 our notice was intended to be unfavorable; for al- 

 though we pointed out some blemishes, as we held 

 them to be, we intended to convey the impression 

 that the substance of the work appeared to us very 

 meritorious : therefore we said that ' the work had 

 been done with evident care and patience,' and men- 

 tioned a long series of observations which might be 



' signalized as being of especial interest and impor- 

 tance.'— Ed.] 



A remarkable new type of mollusks. 



A very remarkable new form of Mollusca has re- 

 cently been submitted to me for examination by Mr. 

 G. W. Tryon of Philadelphia, who received it from 

 Mr. C. R. Orcutt of San Diego, Cal. It was col- 

 lected near that place on a stony bottom, where 

 other bivalves are found in their season, and which 

 appears to be nearly dry at low water. Other speci- 

 mens were received direct from Mr. Orcutt, who col- 

 lected about fifty. This animal is a pelecypod or 

 lamellibranch with an internal shell. Nothing of the 

 sort, or in the least approaching it, has ever been 

 described. 



The animal, from the collector's drawings, is, when 

 living, somewhat of the shape of a small globose 

 Cypraea, of inflated ovoid form, translucent, jelly- 

 like, dotted above with small, rounded papillae, which 

 appear of an opaque white on the general translucent 

 ground. When living, Mr. Orcutt states, it was over 

 an inch in length. The specimens sent have been 

 contracted by alcohol to less than half an inch in 

 length. The mantle which covers the dome of the 

 body is tough and thick : the sides are smooth, and 

 nearly free from papillae. The superior median line 

 is a little depressed. The basal part of the anterior end 

 in life is prolonged beyond the general mass in a wide 

 trough, with the convexity upward, and somewhat 

 expanded at its anterior extremity. About one-third 

 of the way from the anterior end, the mantle is per- 

 forated by an orifice, which pierces it in the vicinity 

 of the mouth. The edges of this orifice project from 

 the general surface, and it is lined with close-set, 

 small papillae. At about the same distance from the 

 posterior end is another tubular perforation, holding 

 a similar relation to the anus; which has, however, 

 plain edges, and is not internally papillose. 



Turning the animal over, we find the anterior 

 trough of the mantle prolonged backward, like a slit 

 with plain edges, to about the posterior third ; from 

 this projects a narrow, hatchet-shaped foot, with a 

 strongly marked byssus-gland at its posterior angle; 

 from this a bunch of white byssus extends to the 

 stone or other object to which this mollusk attaches 

 itself. The cavity of the mantle extends some dis- 

 tance behind the commissure of the pedal opening. 

 The anterior point of the foot is roofed by the trough- 

 like expansion above mentioned. The mouth is pro- 

 vided with two pairs of small palpi. Two gills, very 

 finely microscopically laminate, extend backward from 

 near the mouth, on each side, to the posterior end of 

 the body, the wider one being the inner: between 

 their posterior ends a thin reticularly perforate veil 

 connects the two pairs, and shuts off the anal area 

 from the rest of the mantle cavity. The intestine 

 contains a hyaline stylet, and is considerably convo- 

 luted; but the viscera offer no marked peculiarities 

 when compared with ordinary pelecypods. The shells 

 are enclosed in two little sacs in the substance of the 

 mantle. The umbones are near together, apparently 

 connected by a brown gristle resembling an abortive 

 ligament, and are nearly over the heart. The valves 

 are about ten millimetres long and one millimetre 

 wide, destitute of epidermis, prismatic, or pearly lay- 

 ers. There are no muscular or pallial impressions, no 

 adductors, hinge, or teeth. They resemble in form 

 the exterior of Gervillia, as figured by Woodward, and 

 are pure white. As they lie in the body, they diverge 

 at a rather wide angle from the beaks, forward. The 

 embryonic valves are retained like two tiny bubbles 

 on the umbones. 



