136 BULLETIN 84, UNITED STATES NATIONAL MUSEUM. 



they meet the mouth shields. There are no other plates in the interradial spaces, 

 and this is probably due to the youth of the samples. The genital slits appear as 

 small, oval, and narrow openings, located between the external angle of each mouth 

 shield and the first lateral brachial plate. 



The mouth shields are small and very narrow; they are twice longer than wide, 

 with a verj- obtuse proximal angle and two converging lateral sides wliich meet by 

 a rounded angle; they are compressed between the two large plates which I have 

 just mentioned and the adoral plates. The latter arc very much developed; they 

 are trapezoidal, the proximal side being twice as long as the distal side, and they 

 are contiguous over the whole length of their internal side. The oral plates are 

 small, longer than wide. The oral papilla3 amount to four on each side; the external 

 papilla is extremely large and wide, oval, squamiform, and obhqucly erect; the 

 following three are vciy small, papilliform and conical. The odd terminal papilla 

 is scarcely larger than its neighbors. 



The upper brachial plates are very large, excepting the first one, which is short; 

 they are triangular, much wider than long, with an obtuse and rounded proximal 

 an^le and a more or less convex distal side, which meets the lateral sides by rounded 

 angles. These plates are very much approximated to one another, but not abso- 

 lutely in contact. 



The under brachial plates are little developed, and the first three alone exist. 

 The first plate is narrow and compressed between the two adoral plates; it is lozenge- 

 shaped and longer than wide. The second and tliird plates are rather small, pen- 

 tagonal, a little wider than long, their angles being rounded and not very distinct; 

 they appear less plainly on the smaller than on the larger sample. Beyond these 

 plates, the under face of the arms offers a narrow median stripe of membranous 

 tissue, which is limited on both sides by the side plates. 



The latter are developed chiefly on the arm sides and they do not meet on the 

 median ventral line, but they always remain separated by that stripe of soft tissue 

 which I have just referred to. They carry on their distal side a row of large, rounded, 

 and rough globules, which are hardly longer than wide and amount to four at the 

 base of the arms; these globules represent as many brachial spines and the last 

 globule is somewhat smaller than the others. Within the row formed by the said 

 spines there is a tentacular scale, the shape of which rather recalls that of the brachial 

 spines, although it is more flattened and somewhat shorter than they are. The 

 lateral plates are simple and there is no indication of a supplementary plate. All 

 the plates of the body, as well on the disk as on the arms, are covered with very 

 minute granules. 



Connections and differences. — I refer to the genus Sigsheia the two Ophiurans 

 which I have just described, although their lateral plates are not divided, but this 

 division might appear on older samples; the absence of under brachial plates on 

 the largest part of the arms is evidently a youthful character. By the shape of the 

 upper brachial plates, S. sexradiata recalls S. conifera; which I have just described, 

 but it differs from it in the shape of the plates of the upper face of the disk as well 

 as in the number of arms; this latter character, besides, separates S. sexradiata 

 from the few other species actually knovm of the genus Sigsheia. 



