MOLLUSCS. 



279 



Fig. 300. — Mulinia lateralis. 



Fig. 301. — liart^ia cyrenoides. 



many other fonns. Mactra solidissima occasionally reaches a length of over six inches, 

 has the cardinal teeth delicate, and has & shallow pallial sinus. M. ooalis but rarely 

 exceeds four inches in length, and has the teeth short and 

 the sinus deep. Separated from Mactra proper by an angu- 

 lar pallial sinus is the sub-genus Mulinia, of which one spe- 

 cies, Mulinia lateralis, occurs nearly the whole length of our 

 eastern coast. 



Jiangia (also known as Gnathodon) is a brackish-water 

 genus, represented in the southern United States by the spe- 

 cies M. cyrenoides. In the gulf states this species occurs.in vast numbers. Banks of 



dead shells, three or four feet in thick- 

 ness, occur in many places, some of 

 them twenty miles inland. The city 

 of Mobile is built on one of these 

 banks, while the road over which the 

 inhabitants of N"ew Orleans travel in 

 order to reach Lake Pontchartrain " is 

 made of these shells, procured from 

 the east end of the lake, where there 

 is a mound of them a mile long, fifteen 

 feet high, and from twenty to sixty 

 yards wide ; in some places it is twenty 

 feet above the level of the lake." 

 Tlie family Tellenid^ vies with the Veneridse in its beautifully-colored species. 

 Like the members of that family, they are mostly inhabitants of the warmer seas of the 

 world, the small number of species which stray into the more northern waters 

 being dull colored, and far less attractive than their tropical relatives. The shells are 

 long, compressed, and usually closed and equi-valve ; and one marked feature that is 

 generally found is that the half of the shell in front of the umbones is longer than that 

 behind them. The cardinal teeth are at most two in number ; the lateral teeth are oc- 

 casionally obsolete. The hinge ligament is usually external and posterior. The mantle 

 is widely open in front, and the two very long and slender siphonal tubes are com- 

 pletely separated. The foot is triangular and compressed. In most species the shell 

 is very dense, and highly polished, and not infrequently is white, enlivened by bands 

 or stripes of delicate shades of red or yellow, while in others the effect is heightejied 

 by the finely sculptured lines. 



In Tellina, which reaches its highest development in the Indian Ocean, the shell is 

 rounded in front and angular posteriorly, a fold running from the angle to the umbo. 

 The siphons are very long, and can be extended to at least twice the length of the 

 shell, and, as a necessary sequence of such extensibility, the pallial sinus is very wide 

 and deep. In Strigilla the surface is ornamented with 

 divaricating lines, like those of Cyclas, described on a pre- 

 ceding page. 



Our northern forms belonging to this family are dull 

 colored and unattractive. Tellina tenera, which occurs from 

 Florida to the Gulf of St. Lawrence, is an exception, for the 



delicate rose-color which tinges the otherwise white shell makes it an object of 

 beauty. The siphons are very long, several times the length of the body, and hence 



Fig. 302. — Tellina tenera. 



