154 THE NAIADES OF MISSOURI 



to a plicate shell. This byssal thread was so strong that it pulled 

 off with some difficulty and was split in three strands near its 

 base, each being marked by a muscilaginous substance. The 

 umbonal markings of this flat straw-colored juvenile shell consists 

 of four broadly inverted V-shaped ridges the rear line being finer, 

 longer and closer together, extending down the posterior umbonal 

 ridge. 



Miscellaneous Remarks: — L. jragilis is distinctly a river 

 form for this State, although we would naturally think that this 

 f^p- ' alated and thin-shelled species would be established in the lakes 



[ and other quiet waters of Northwest Missouri, especially where 



it predominates the streams. Breeding records for this species 

 show that it may bear glochidia every month of the year except 

 for a few weeks in mid-summer; hence, a very long period breeder. 

 It was found in August distending its ovisacs with water preparatory 

 to ovulation. Only two other species possess smaller glochidia — 

 those of Amygdalona]as donacijormis (L,ea) and A. elegans (Lea) 

 with yvhich. jragilis is closely related; however, external characters 

 of shell alone — especially as to size and form — show no close con- 

 nection. Fragilis may be distinguished from other similar alated 

 forms by its peculiar yellow surface, marked by brown horn-colored 

 restlines, depressed umbones, green rays in young and broadly 

 elliptical outline in old specimens, if their alae are lost as is often 

 the case. Through special cooking tests the writer has found 

 out that nearly all the soft parts of this species is very edible. 

 It is also economically important in producing pearls, since it is 

 easily parasitized. No mussel is more active and as it anchors 

 itself so firmly it is often extracted from its bed with great 

 difficulty. The straw-colored and green rayed juveniles are easily 

 located, not so much by color as by their "tracks" since they are 

 the most active crawlers. This species is the most abundant in the 

 One-Hundred-and-Two, Platte, Grand, Tarkio, Osage — in fact all 

 the streams of Northwest and Central Missouri as determined by 

 personal collections. It is poorly developed in the Osage and is not 

 found at all further South in the clear- water streams of the Ozarks. 

 Simpson reports it for the Missouri River, but I think he means 

 only for the tributaries of the Missouri as no mussel life is actually 

 reported in the main stream of this River throughout the State. 

 Its general distribution is for the entire Mississippi River drainage; 



