159 



terminates in a sharp point, and the upper part is so worn on the 

 inside as to be triangular. When the animal to which this cra- 

 nium belonged was taken, he was very much emaciated, and 

 moved with much difhculiy. 



In neither of these cases was there any appearance of disease 

 except that caused by the distortion itself. 



The President remarked that instances of distortion of the in- 

 cisors among the rodent animals is by no means uncommon. 

 Many of these, affecting different species, may be found recorded 

 in the books. The incisors of the two jaws are placed in oppO' 

 sition to each other, and by their mutual pressure, seem to re- 

 strain each other's growth. When, by accident, either of the 

 teeth is turned aside from its natural direction, the antago- 

 nistic power is removed, the growth of the tooth proceeds without 

 restraint, and the animal is soon unable to bring their points into 

 opposition. As these teeth are its main instruments of procuring 

 food, it becomes unable to procure a full supply, and sooner or 

 later dies of hunger, often it may be supposed in the ;nidst of 

 plenty. 



Dr. Gould gave descriptions of the following new species of 

 Rinfiula, Crepidula, Caiyplra^a, Hipponix, and Pileopsis, from 

 the collection of the United States Exploring Expedition. 



RiMULA cucuLLATA. Tcsta soUda, cinerea, per-inequilateralis, 

 costis ad 40 acutis, compressis, majoribus et minoribus alternanti- 

 bus radiata, et striis concentricis confertis muricata ; apice ele- 

 vato, acuto, adunco, prorsum spectante : fissura lanceolata : aper- 

 tura ovata ; margine sulcis iuequalibus alternantibus crenulato : 

 facies interna porcellana ; fornice tenui, simplici, arcuato. Long. 

 I, lat. iV, alt. t poll. Hab. Puget Sound. 



A large and curious species, its very inequilateral form giving 

 it the aspect of a Hipponix. It is less elevated in proportion to 

 its base than any other known species. The ribs are very regu- 

 lar, and sometimes still finer rays are found in the interstices. 



RiMULA GALEATA. Tcsta solida, cinerea, elevata, globoso-coni- 

 ca, apice central!, acuto, prorsum porrecto, striis filiformibus con- 

 fertis radiata, et striis minoribus concentricis decussata : fissura 

 brevis, fusiformis : apertura rotundato-ovalis ; margine expanse, 



