40 



THE NAUTILUS. 



having growing on them a shell of the salt water mussel (Mytilus)} 

 both host and mess-mate were alive when taken. 



The G. rotundata were unusually fine, the shades of color exhib- 

 ited by them I have never seen excelled. These were otherwise in- 

 teresting as a number of them were gravid, and we felt all the im- 

 portance of being true discoverers, as no student had ever before 

 noted them in this condition. As regards this part of their physi- 

 ology they are a true Lampsilis. The possession however of several 

 unique characteristics will probably keep them in a separate genus. 



Mention was made above of a new variety of Q. trapezoides. 

 This shell differs from the type in having its dorsum very much 

 arched or bent midway. The posterior is widely biangulated. The 

 anterior is singularly truncated like W. comscus, Gld. The effect 

 being that the outline forms nearly an equilateral pentagon, hence the 

 name. Aside from its form, it differs in being much smaller, and 

 frequently entirely devoid of plication on either its sides or posterior 

 slope. A striking peculiarity is that the posterior end of the liga- 

 ment is perpendicularly over the centre of the base, whereas in the 

 ordinary trapezoides the end is situated about three-fourths of the 

 distance from the anterior to the posterior. 



LIST OF SHELLS COLLECTED ON SAN MARTIN ISLAND, LOWER 

 CALIFORNIA, MEXICO. 



BY FRED. BAKER, M. D. 



Loligo sp? Giant squid. 

 Cavolina tridentata Gmel. 

 Cerostoma nuttalli Conr. 

 Ocinebra circumtexta Stearns. 

 Ocinebra gracillima Stearns. 

 Ranella californica Hds. 30 



fathoms. 

 Fusus luteopictus Dall. On 



breakwater at low tide. 

 Macron kellettii A. Ad. 

 Macron lividus A. Ad. 

 Nassa fossata Gld. 

 Nassa perpinguis Hds. 



Monoceros lugubre Sby. 

 Marginella regularis Cpr. 30 



fathoms. 



Marginella jewettii Cpr. Drift. 

 Marginella pyriformis Cpr. 

 Volvarina varia Sby. Drift. 

 Olivella biplicata Sby. 

 Astyris gouldi Cpr. 30 fathoms. 

 Astyris aurantia Dall. 

 Astyris gausapata Gld. 

 Astyris carinata, var. hindsii Rve. 

 Astyris tuberosa Cpr. 

 Anachis penicillata Cpr. 



