450 PROCEEDINGS OF THE ACADEMY OF 



D. S m i th ii, Tryon. 



Testa brevi, ovata, in medio oblique divisa, antice acute striata, 

 postice paulo striata vel laevigata; lamina umbonali ovata, postice 

 subtrnncata, antice rotundata, lamina- anteriori parva, antice sub- 

 acuminata. 



Shell short, ovate, divided in the middle by an oblique impressed 

 line, posterior to which tbe surface is covered with growth lines 

 only, but anteriorly it is finely and sharply transversely sculptured, 

 and obsoletely radiately ribbed in some specimens. 



Tbe umbonal plates are generally much distorted, so that no particular form 

 can be traced throughout all the specimens, though the more perfect approach 

 to that depicted in the magnified figure above. 



Length -6 ; height and breadth -4 inch. 



Collections of Acad. Nat. Sci Smithsonian Institution, Sanderson Smith, 

 New York ; Hugh Cumming, London; Geo. W. Tryon, Jr. 



Habitat. Tottenville, Staten Island, burrowing in oyster shells. 



Mr. Smith, to whom I am indebted for the opportunity of examining numer- 

 ous individuals of this curious species, gives the following interesting infor- 

 mation in relation to them : 



; ' The shells were all dead, and I have found as yet no positive evidence of 

 the oysters being imported ones, although from the great number of southern 

 oysters planted in Prince's Bay and the neighborhood, there is a considerable 

 probability of this. The large number of oyster shells which have been 

 bored from the inside, and consequently after the death of the oyster, suffices 

 to show that the shell is now, or very recently has been living here, as it is 

 hardly likely that so many large dead shells would have been accidentally 

 brought with the living ones. I have hitherto found them only in one lot of 

 thirty or forty loads of shells, of which I cannot ascertain the exact source. 

 They are by no means scarce, and several hundred specimens must have been 

 obtained by myself and others." 



From the condition of the dried animal matter contained in some of the spe- 

 cimens, I quite agree with Mr. Smith's conjecture that the species is probably 

 still living at the locality mentioned. In many cases where this species has 

 bored from the outside of the oyster shell, penetrating entirely through its or- 

 dinary surface, the oyster has protected itself from contact by depositing a 

 layer of nacre between itself and the exposed portion of the intruder. 



Dactylina (Gitocentedm) Chiloensis, King. 



To the synonymy of this species must be added Pholas (Dactylina) retifer. 

 Morch. Mai. Blatt. vii. p. 177, Dec. 1860. 



Description. T. elongato-cylindracea fere clausa, antice rotundato subpro- 

 ducta, postice elongata planata laeviuscula ; costae 25 parum prominentes lon- 

 gitudinalibus validioribus decussatae, intersectionibus squamiferis; costae sub- 

 sequales, quarta antica parvula; interstitia costarum lirulis planis 4-5 ; costae 

 anticae et lirulae intermediae validiore 5 , fascie interna excavate; lamina dor- 

 ealis reflexa unde late umbilicata ; cellular dorsales ad num. 12 inaequales. 



Long 104, alt. 33 mill. Realejo, valva solitaria dextra fractra." 



The intermediate flat ribs or lirulae mentioned above and considered by 

 Mcirch to be a distinctive character, are very apparent at the anterior end of 

 most perfect and fresh valves of C h i 1 o en s i s, and they are frequently marked 

 internally by corresponding sulcse ; as the shell grows to maturity these riblets 

 bfcome obsolete, or are replaced by a siDgle intermediate squamiferus small 

 rib. 



There is no regularity in the number of radiating costae on the surface, though 

 they do generally average twenty-five in number; but in some valves they be- 

 come evanescent posteriorly sooner than in others. The dorsal cellules num- 

 ber in different specimens before me from 12 to 15. 



[Sept. 



