1869.] 109 [Perkins. 



two fifths of the width of the aperture ; columella showing two rather 

 obtuse teeth or folds, the upper being the largest, with a sinuous 

 sulcation at their bases, parallel to the outline of the columella, 

 causing, together with the folds, an appearance resembling the thread 

 of a screw, or the plaits in Cancellaria. 



Length .11 inch. Breadth .06 inch. 



Habitat: Littoral zone, Rocky point, Tampa Bay, western shore 

 of Florida; found with other small species of mollusks upon the un- 

 der side of clumps of "Coon oysters" at low water line. Two speci- 

 mens, living, one adult, the other not quite developed. 



This well marked species is the first of the genus found upon the 

 eastern side of the Continent, and the fourth thus far detected in 

 North America. 



The late Prof. C. B. Adams obtained a species at Panama, P. an- 

 gulatus, Mr. W. G. Binney described another, P. lirata, from Cape 

 St. Lucas, and Dr. J. G. Cooper a third, P. unisulcata, from San 

 Pedro, California; the species above described is more globose, and 

 more delicate than either of the others. 



For the excellent figure of P. naticoides I am indebted to the 

 kindness of my friend, Mr. E. S. Morse. 



Molluscan Fauna of New Haven. A critical review 



OF ALL THE MARINE, FRESH WATER AND LAND MOLLUSCA 

 OF THE REGION, WITH DESCRIPTIONS OF MANY OF THE LIVING 

 ANIMALS AND OF TWO NEW SPECIES. PART I. CEPHALOPODA 



and Gasteropoda. By George H. Perkins, Ph.D. 



New Haven Bay, in and about which most of the marine species 

 mentioned in the following pages were collected, is an arm of Long 

 Island Sound, nearly five miles long and, at the entrance, three 

 broad. 



Near the shore the water is shallow, and nowhere is the depth, at 

 low tide, more than three fathoms. The average depth over the 

 whole area is less than two fathoms. 



Three small rivers, emptying into the bay, freshen the water and 

 fill it with mud, which covers most of the bottom, and even where 

 that is sandy there is more or less mud mingled with the sand. 



Near the lighthouse, at the entrance of the bay, on the eastern 

 side, and for a mile northerly, a low ridge runs near the water's 

 edge, and on the western side, nearly opposite the lighthouse, are a 

 few masses of rock of no great extent, which are together often 



