so 



home and abroad, now concur in abolishing' the 

 new genu?, and placing the so called Welling- 

 tonia gigantea in the old genus Taxodium. re- 

 taining the specific name giganteuiti. 



Dr. II. 6. also presented specimens of Trillium, 

 Asarum, and other plants, from Alameda county. 



Col. R. D. Cutts presented the skin of a Fox. 



Messrs. Ellery & Doyle presented an antiqua- 

 ted work on Natural History, published at Ed- 

 inburgh, in the last century. 



Fed. 19. 1855. 



Col. L. Ransom, Vice President, in the chair. 



Col. R. D. Cutts. of the C. S. Coast Survey 

 was elected corresponding member; 



H. C, Bloomer, Wm. ffeffly, Dr. A. Kellogg, 

 were elected Library Committee. 



Donations. Report of the Smithsonian Insti- 

 tute, for 1854, presented by the Institute. 



Dr. Bohr, presented a species of Xepa. 



Dr. J. B. Trask, read the following paper on a 

 new species of Alasmodou, from the Yuba Riv- 

 er. He also presented three specimens of the 

 shell. 



Alasmodou Yubaeasis, Trask. — Shall, thick. 

 transversely elongate; umbones low, situated 

 rather below the line of the hinge margin, and 

 near the middle of the anterior third, very much 

 eroded, hinge and veutral margin unequally curv- 

 ed, shell broader before than behind, anterior 

 margin bluntly and regularly rounded, slightly 

 obtuse below, dorsal margin and ligament rather 

 flatly arched, (in young shells the dorsal line from 

 the end of the ligament posteriorly is often angu- 

 late) posterior margin obtusely rounded in ma- 

 ture specimens, its superior portion comprising the 

 posterior third truncated, or but very slightly 

 arched ; edge of the valves thick anteriorly and 

 rounded, thin posteriorly and rather sharp, slight- 

 ly everted, shell gaping at both ends, (in young 

 specimens the valves at the posterior end are 

 closed) broader before than behind, considerably 

 inflated from the umbones along its posterior alo] ie, 

 epidermis nealy black, opaque, smooth toward 

 the beaks, rather roughly corrugated from the 

 middle of the disks to the margins, surface undu- 

 lated with annual lines of growth. Wathin, 

 smooth ; color lilac-greenish and iridescent poste- 

 riorly; rayed upon the surface beyond the pallial 

 line, and seen by direct or transmitted light ; car- 

 dinal teeth one in each valve, erect, that in the 

 right valve sub-connate, bluntly rounded at the 

 a P ex . grooved on the upper part, pitted at the 

 posterior base, tooth in the left valve erect, flat. 

 sub-triangulate, three small oblique grooves upon 

 ita upper surface producing small denticulatkms 



on the edge : five small transverse grooves on the 

 under surface; tooth sub-acutely pointed; pallial 

 line impressed anteriorly, obsolete posteriorly; 

 anterior cicatrices distinct, deep, posterior conflu- 

 ent, shoal; nacre not extending to the margins, 

 leaving a narrow border surrounding the latter: 

 a somewhat tumid elevation of the shell between 

 the pallial line and margin anteriorly. Length, 

 four and five twentieths inches: height, one and 

 six tenths; breadth, oue. 



The habitat of this shell is the Yuba River. 

 and the specimens on which this description is 

 based were taken from that stream about forty 

 miles above its confluence with the Feather, by 

 Hon. C. E. Lippincott, from whom they were 

 procured. The shells are somewhat abundant, and 

 have often been found at considerable depths in- 

 bedded in the gravel drift of that stream. There 

 are shells of this genus in many of the running 

 streams of this country, but thus far there seems 

 but little diversity in the species, with the excep- 

 tion perhaps of the more northern rivers. 



This shell represents A. arcuatn, of the 

 Atlantic coast, but differs from that shell as de- 

 scribed by Dr. Gould, and also from the descrip- 

 tion of Dr. DeKay. The particulars which 

 separate it from the Atlantic species are the fol- 

 lowing: A. iircuata, has two cardinal teeth in 

 the left valve; our species has but one, or even 

 a deuticulation on that valve that, could be con- 

 sidered even rudimentary. The form in the oue 

 is pyramidal and has from three to five grooves, 

 while the California shell is flat and sub-triangu- 

 late, having scarcely three distinct grooves upon 

 its surface, which is a constant character. — 

 The tooth in the right valve is erect and has no 

 twist as that described in the Atlantic species. 



The beaks in our species are situated near 

 the middle of the anterior third, and their sum- 

 mits are below the line of the hinge margin, and 

 it is much broader before than behind; the color of 

 the inner disks being so distinct from that of the 

 Atlantic species, and the rays visible on the in- 

 ner surface beyond the pallial line, are sufficient 

 with the above to separate our shell from those 

 east of the Rocky Mountains. 



The difference of climate and the space of a 

 broad continent between, would have the effect 

 to produce wide differences in specific character 

 of allied genera. I therefore consider this spe- 

 cies as ondescribed and have selected the 

 name of the stream from which it was taken, 

 for its specification. 



The corresponding secretary, read a letter from 

 Dr. D. W. Hatch of Sacramento, in which he 

 promises a copy of his Meteorological Journai, 

 and one from Prof. Nooney. dated at Washing- 

 ton, recommending the Society to send copies of 

 the Bulletin, to the Smithsonian Institute for ex- 

 change with foreign scientific bodies. 



